Mechanical Systems and Plans

Engineering techs are often called upon to develop drawings for projects. To be able to perform that task successfully, you need to be familiar with the various systems a structure may incorporate to meet the use for which the structure is designed.

Each trade discipline has its own unique requirements, constraints, routings, materials, and methods. Each trade discipline also has its own unique symbols for communicating the information to drawings for common understanding by all involved in a project.

Your accurate drawings could support a project at a number of stages: planning, cost analysis, installation, quality control, or final inspection. This lesson will acquaint you with the water distribution and drainage aspects of mechanical systems, otherwise known as plumbing.

When you have completed this lesson, you will be able to:

1. Describe the different types of mechanical plumbing systems.
2. Interpret different types of mechanical plans.



  1. Mechanical Systems (Plumbing)
  2. Mechanical Plans
Review Questions


In general, mechanical systems include heating, ventilating, and air conditioning (HVAC), piping, refrigeration, and air filtration as well as plumbing.

Plumbing, itself, is the system of pipes, fixtures, and other appurtenances that supply water to a structure from a source such as a water main, and remove it with any associated waterborne wastes to a destination such as a sewer main, septic tank, or cesspool.

An appropriately functioning plumbing system brings a supply of safe water into a structure and distributes it for drinking, cooking, washing, industrial application, or any other use required to meet the structure’s design needs. It then carries the water away, along with any waste materials combined with the water, without posing a health hazard to the users.

The National Plumbing Code is widely accepted as a guideline for plumbing design minimum requirements. However, additional codes, regulations, and trade practices vary from one location, or even place of application to another, and define the plumbing specifications for an individual project. Therefore, you must also be familiar with applicable local codes, especially when working with mechanical drawings and plans.

1.1.0 Water Distribution System

The purpose of a water distribution system is to carry potable cold and hot water throughout a building for domestic or industrial use. A typical water supply system (Figure 9-1) consists of:

Figure 9-1 — Typical water supply system.

The water service pipe begins at the water main.

The water distribution pipe starts at the end of the service pipe and supplies the water throughout the building. 

1.1.1 Piping Materials

 Several types of pipe are available for water distribution systems, but Seabees commonly use copper, plastic, galvanized steel, or cast iron. Of those, plastic is becoming the most common for both civilian and military use due to the lower cost of materials and ease of installation with its associated lower labor costs. Copper Pipe and Tubing

Traditionally, copper has been one of the most widely used materials for tubing. It does not rust and is highly resistant to accumulation of scale particles in the pipe. Copper pipe is manufactured in six grades and thicknesses, three of which are appropriate for water distribution systems from water main to tap; types K, L, and M.

Figure 9-2 shows some typical fittings for copper tubing. The connections between the fittings are made with solder. Soldering allows all the tubing and fittings to be measured, cut, and set in place before the joints are finished. Generally, this allows faster assembly and completion.

Figure 9-2 — Typical copper fittings.

Copper is durable and connects well to valves. However, copper should not be installed if the water has a low-pH (high acidic) level, common to many private well systems. (Figure 9-3)

Figure 9-3 — pH scale.

Per Washington State University Department of Ecology:

“The pH scale measures acidic and alkaline materials in water. On this scale, 7.0 is the neural point, indicating a perfect balance between the two. Acidic pH values are below 7.0, and alkaline pH values are above 7.0.

In areas where groundwater trickles through limestone, carbonic acid and limestone form soluble bicarbonates, neutralizing the acid. The result is alkaline water that is usually hard, has low carbon dioxide concentrations, and pH values between 7 and 8.

Where underground strata do not contain limestone, groundwater retains acidity, has pH values between 6 to 7, (sic) and corrodes metals used in plumbing.”

To quote the Environmental Protection Agency:

“There are two types of copper corrosion: uniform and nonuniform. Both types are caused by certain characteristics of water chemistry…”

Uniform corrosion is identified by the presence of a relatively uniform deposition of copper corrosion by-products across the inner surface of a pipe wall and is typically associated with elevated copper levels at our taps.

Nonuniform corrosion, or pitting, is the isolated development of corrosion cells across the inner surface of a pipe wall. Although pitting (Figure 9-4) corrosion is seldom associated with elevated levels of copper at our taps, excessive pitting corrosion can lead to “pinhole” leaks in the pipe, which could result in water damage and mold growth."

Figure 9-4 — Example of copper pitting.

Water below PH 6.5 is considered acidic and may begin to pit the copper and create pinhole leaks. The majority of public utilities supply water at a PH between 7.2 and 8.0. Plastic Pipe

Plastic pipe is rapidly replacing copper as the material of choice in both civilian and military applications. (Figure 9-5) It has a number of advantages over both copper and steel piping:

Figure 9-5 — Typical plastic pipe fittings.

Polyvinyl chloride (PVC) is one of the most versatile plastic and polyvinyl resin pipes. Made of tough, strong, thermoplastic material, PVC has an excellent combination of physical strength and chemical resistance properties.

Chlorinated polyvinyl chloride (CPVC) is a stiffer design for greater resistance to impact and to temperature extremes. You can use CPVC for cold-water systems and hot-water systems with temperatures up to 210°F.

The principal mechanical difference between CPVC and PVC is that CPVC is significantly more malleable, allowing greater flexibility and crush resistance. CPVC also requires a special solvent cement application. For water supply, distribution, and sewer drainage systems, plastic pipe is becoming increasingly popular for its economy, ease of installation, and lack of maintenance requirements. Galvanized Pipe

Still used but less often, galvanized (coated with zinc) pipe (Figure 9-6) can provide the water service and distribution inside a building for hot and cold fixtures. Manufactured in 21-ft lengths, it is galvanized both inside and outside at the factory to resist corrosion. However, galvanized pipes still have a tendency over time to build up enough scale inside the pipe to reduce water flow in gallons per minute. Galvanized pipe sizes are based on nominal inside diameters, which vary with the thickness of the pipe. Galvanized pipes require threaded connections so outside diameters remain constant for standard fittings.

Figure 9-6 — Standard galvanized pipe fittings. Cast-Iron Water Pipe

Frequently used for water mains and service pipe up to a building, cast-iron pipe (Figure 9-7) is sometimes called cast iron pressure pipe. Unlike cast iron soil pipe, cast-iron water pipe is manufactured in 20-ft lengths rather than 5-ft lengths.

Figure 9-7 — Standard cast-iron pipe fittings.

Besides bell-and spigot joints, cast-iron water pipes and fittings are made with either flanged, mechanical, or screwed joints. The screwed joints are used only on small diameter pipe.

1.1.2 Fittings

The size of the pipe connection to the openings identifies fittings. For example, a 3- by 3- by 1 1/2-in. tee is one that has two openings for a 3-in. run of pipe and a 1 1/2-in. reduced outlet. If all openings are the same size, only one nominal diameter is designated. For example, a 3-in. tee is one that has three 3-in. openings.

Fittings vary according to the type of piping material used, along with the appropriate joint sealing/connecting material, but the general shapes for each are typical.

There are: elbows, tees, unions, couplings, caps, plugs, nipples, reducers, and adapters. Some plastic pipes can also be adapted to metal pipe fittings.

There are two types of malleable iron or cast iron pipe fittings used for steel pipe or wrought iron: the pressure type and the recessed type (Figure 9-8).

Figure 9-8 — Pressure fitting and Recessed fitting.

A pressure fitting is the standard fitting used on water pipe. A recessed fitting, also known as a cast-iron drainage or Durham fitting, is generally required on all drainage lines. With its smooth joint fitting, it reduces the probability of grease or foreign material remaining in the joint to build up and cause a stoppage. As drainage lines, recessed fittings are designed so that horizontal lines entering will have a slope of ¼ in. per ft. Elbows (or Ells) 90° and 45°

Elbows (Figure 9-9) change the direction of the pipe either 90 or 45 degrees. Regular elbows have female threads at both outlets.

Figure 9-9 — Copper 45º elbow.

Street elbows (Figure 9-10) change the direction of a pipe in a close space where it would be impossible or impractical to use an elbow and nipple. Both 45- and 90-degree street elbows are available with one female and one male threaded end.

Figure 9-10 — CPVC 90º street elbow.

The reducing elbow (Figure 9-11) is similar to the 90-degree elbow except that one opening is smaller than the other.

Figure 9-11 — Galvanized 90º reducing elbow. Tees

A tee (Figure 9-12) connects pipes to change the direction of a pipe run. They may be of different diameters. A straight tee has a straight-through portion and a 90- degree takeoff on one side. All three openings of the straight tee are the same size.

Figure 9-12 — Cast iron tee with flanges. 

A reducing tee (Figure 9-13) is similar to the straight tee except that one of the openings is of a different size than the other.

Figure 9-13 — Copper reducing tee. Unions

There are two types of pipe unions. Both join two pipes together but are designed for easy disconnection. A ground Joint Union (Figure 9-14) consists of three pieces.

Figure 9-14 — Galvanized ground joint union.

A flange union (Figure 9-15) has two parts.

Figure 9-15 — Cast-iron flange union. Couplings

There are three common types of couplings. The straight coupling (Figure 9-16) is for joining two lengths of pipe in a straight run. A run is that portion of a pipe or fitting continuing in a straight line in the direction of flow.

Figure 9-16 — CPVC straight coupler.

A reducer (Figure 9-17) joins two pipes of different sizes.

Figure 9-17 — Copper straight reducing coupler.

The eccentric reducer (Figure 9-18) joins pipes of different sizes so the two pieces of pipe will not be in line with each other. It provides optimum drainage of the line.

Figure 9-18 — Cast-iron eccentric coupler with flanges. Caps

Used like a plug, a cap (Figure 9-19) is a fitting with a female (inside) sizing to fit over the pipe diameter. For some pipe materials, caps are threaded.

Figure 9-19 — A-Galvanized cap. B-Copper cap. Plugs

Plugs (Figure 9-20) are fittings with male (outside) threads. They screw into other fittings to close openings. Plugs have various types of heads, such as square, slotted, and hexagonal sockets

Figure 9-20 — A-CPVC octagonal head plug. B-Galvanized square head plug. Nipples

A nipple (Figure 9-21) is a length of pipe with a male thread on each end. It is used for extension from a fitting.

Figure 9-21 — A-Brass close nipple. B-Galvanized 10 ft. nipple.

At times, you may use the dielectric or insulating type of fittings. (Figure 9-22) These fittings connect underground tanks or hot-water tanks. They are also used to join pipes of dissimilar metals. The purpose of dielectric fittings is to curtail galvanic corrosion or electrolytic action. The most common dielectric fittings are the union, coupling, and bushing.

Figure 9-22 — Typical dielectric union.

1.1.3 Joints and Connections

There are various methods of joining pipes for water distribution systems. Each method is designed to withstand internal (hydrostatic) pressure in the pipe and normal soil loads if joints and connections are belowground. Some of these methods produce the types of joints and connections described below. Flared and Sweated Joints

Used with copper pipe and tubing. The end of a copper pipe forms into a funnel-like shape so that it can be held in a threaded fitting. (Figure 9-23) This method is flaring, and the result is called a flared joint.

Figure 9-23 — Typical flared joint.

A sweated joint (Figure 9-24) uses soft solder instead of threads or flares. This method joins the metals at the 450-800º range.

Figure 9-24 — Typical sweated joint.

Occasionally, copper pipe or tubing is fused by heating with a gas flame and silver-aIloy filler metal. This is silver brazing (or hard soldering) (Figure 9-25) and done at temperature ranges of 1100- 1600º.

Figure 9-25 — Typical silver brazed joint. Solvent Welded, Fusion Welded, Fillet Welded, Threaded, and Flanged Joints

Used with plastic pipes. A solvent welded joint (Figure 9-26) involves applying a primer and the solvent cement. Before applying the primer and solvent, the pipe and fitting must be at similar temperatures; do not undertake this fitting when the temperature is below 40°F, above 90°F, or when the pipes are exposed to direct sunlight.

Figure 9-26 — Typical solvent welded joint.

In fusion welded joints, (Figure 9-27) a gas or electrically heated welding tool simultaneously heats the meeting surfaces of the pipe and fitting to a uniform plastic state. The two components are joined together to fuse in a homogeneous bond and allowed to cool.

Figure 9-27 — Typical fusion welded joint.

Fillet welded joints (Figure 9-28) are made with uniform heat and pressure on a welding rod during application of a bead. This process can also repair leaks in thermoplastics.

Figure 9-28  — Making fillet welded joints.

Threaded joints (Figure 9-29) are commonly used for temporary and low pressure piping since threading reduces the pipe wall thickness. Teflon tape is often used for pipe joint compound.

Figure 9-29 — A-CPVC threaded joint. B-Teflon tape.

Flanged joints (Figure 9-30) are for process lines that are dismantled frequently. They join plastic flanges together with soft rubber gaskets.

Figure 9-30 — Typical flanged joint ad gasket. Bell-and-Spigot and Mechanical Joints

Used with cast-iron pressure pipe and fittings for water mains. Bell and spigot lines (Figure 9-31) may be joined by the use of lead, lead wool, or sometimes a sulfur compound.

Figure 9-31 — Typical bell and spigot joint.

Mechanical joints (Figure 9-32) are made with rubber sealing rings held in place by metal follower rings that are bolted to the pipe. These permit expansion and contraction of the pipe without injury to the joints.

Figure 9-32 — Typical mechanical joint. Threaded Pipe Joints

Galvanized steel, galvanized wrought iron, and black-iron pipe only use threaded joints. The process includes connecting threaded male and female ends. Nontoxic compounds (Figure 9-33) are used for thread lubricant on water pipes, while powdered graphite and oil are used for steam pipes.

Figure 9-33 — A-Typical threaded joint. B-Pipe joint compound.

1.1.4 Valves

Valves stop, start, or regulate the flow of water into, through, or from pipes. Essentially, valves consist of a body containing an entrance and an exit with a means of stopping the flow in between with a disk or plug tightly pressed against a seating surface. There are many different valve designs, but this lesson will discuss only the three most common: gate, check, and globe Gate Valve

A gate valve is a linear motion valve used to start or stop fluid flow; it does not regulate or throttle flow. The gate valve may have a wedge-shaped movable plug, or a (single or double) round disk that fits tightly against the seat when the valve is closed. (Figure 9- 34)

Figure 9-34 — A-Wedge gate valve.

When the gate is open, it provides unrestricted flow. It allows fluid to flow through in a straight line with little resistance, friction, or pressure drop, provided the valve gate or disk is kept fully open. B-Disk gate valve. A gate valve releases a variable amount with each turn of the gate but must always be operated in either the fully open or fully closed position. A partly closed gate will cause vibration and chattering, damaging the seating surfaces. Check Valve

A check valve is used to prevent backflow in pipelines. They are entirely automatic and used where the flow of liquids, vapors, or gases is required in one direction only. Check valves fall into two main groups: swing check valves (Figure 9-35) and lift check valves. (Figure 9-36)


Figure 9-35 — Typical swing check valve.

A lift check valve is usually used for air or gases or when a check valve is operated frequently. A swing check valve is used for unrestricted flow.


Figure 9-36 — Typical lift check valve. Globe Valve

The globe valve, (Figure 9-37) so-called because of its globular-shaped body, regulates the flow of liquids, gases, and vapor flow by means of throttling (adjusting rate of flow). They are well suited for services requiring regulated flow and/or frequent valve settings (throttling).


9-37 — Typical globe valve.

1.1.5 Pipe Supports

Structurally, pipes are only designed to withstanding normal soil loads and internal pressures up to their hydrostatic pressure rating. Therefore, any pipe aboveground or in the interior of buildings supplying air, water, or steam, must be adequately supported to prevent sagging. The weight of the pipes plus the weight of fluid contained in them may produce strained joints and breaks that can cause leaks in the valves. Figure 9-38 shows several methods of supporting pipe within a structure in both horizontal and vertical positions.


Figure 9-38 — Typical pipe supports within a structure.

On water mains, thrust blocks (Figure 9-39) made of concrete or other applicable materials, are installed at all changes of direction to prevent pipe displacement caused by the movement of water under high pressure.


Figure 9-39 — Typical thrust block application.

1.1.6 Pipe Insulation

Insulating the pipelines helps prevent heat passage from steam or hot-water pipes to the surrounding air or from the surrounding air to cold-water lines. In some cold regions, insulation prevents water from freezing in a pipe, especially when the pipe runs outside a building. Thus, hot-water lines are insulated to prevent loss of heat, while potablewater (drinking water) lines are insulated to prevent absorption of heat. Insulation also subdues noise made by the flow of water inside pipes, such as water closet discharges. Figure 9-40 shows some typical pipe insulations.


Figure 9-40 — Typical pipe insulation.

1.2.0 Sanitary Drainage System

A drainage system carries sewage, rainwater, or other liquid wastes to a point of disposal. There are three types of drainage systems—storm, industrial, and sanitary. While a storm or industrial drain system is not out of the scope of a large Seabee project, the most common tasking is for installation of a sanitary drainage system. A properly functioning sanitary drainage system carries sanitary and domestic wastes from a source (or collection system) to a sewage treatment plant or facility without collecting any additional surface water or groundwater. This prevents overload of the treatment facility.

1.2.1 Piping Materials

The type of material used for piping depends on location and availability as well as whether the installation is:

Like water distribution systems, the growing popularity of PVC piping for sanitary drainage is its Cast-Iron Soil Pipe (CISP)

This type of pipe is composed of gray cast iron made of compact close-grained pig iron, scrap iron and steel, metallurgical coke, or limestone. (Figure 9-41) CISP is normally used in or under buildings; it usually protrudes at least 5 ft from the building to connect to a concrete or clay sewer line.


Figure 9-41 — Single hub cast-iron soil pipe (CISP) with cutter.

Cast-iron soil pipe is also used under roads or other places of heavy traffic. If the soil is unstable or contains cinder and ashes, vitrified clay pipe is used instead of cast-iron soil pipe. Vitrified Clay Pipe (VCP) and Concrete Pipe

Vitrified clay pipe (VCP) (Figure 9-42) is made of moistened, powdered clay processed to a very hard, inert, glass-like state. VCP is used for house sewer lines, sanitary sewer mains, and storm drains.


Figure 9-42 — Vitrified soil pipe (VSP) spigot and hub.

Unreinforced concrete pipe is used to meet the requirements for sewer drainage in the smaller sizes —those less than 24 in. However, reinforced concrete (Figure 9-43) pipe is also available in elliptical as well as round shape with diameters from 1- to over 12-feet.


Figure 9-43 — Concrete pipe. Plastic Pipe

Rigid polyvinyl chloride pipe (Figure 9-44) application has expanded greatly over the years for use in underground sanitary sewage systems. At one time, plastic piping was primarily for limited industrial and domestic uses such as farm water and lawn sprinklers systems.


Figure 9-44 — Rigid plastic sewer pipe.

Plastic pipe is used for all kinds of water and drainage applications. It has the following qualities:

1.2.2 Fittings

Fittings for sanitary (waste) drainage systems (Figure 9-45) are similar in shape to those used for water distribution systems. However, as in water distributions systems, a system’s various fittings can be the same general shape, but vary in specific details according to the type of piping materials used. Special mechanical seal adapters are also available for joining different types of pipes, such as cast-iron soil pipe to vitrified clay pipe, or vice versa.


Figure 9-45 — Typical sanitary pipe fittings - bends and reducers. Bends

A bend is termed by either a fraction or a degree. The fraction term is a fraction of a 360º radius. Thus, a 1/16 bend is a 22 1/2º turn, a 1/8 bend is 45º, and a 1/4 bend is 90º. There are also short-radius and long-radius fittings available as well as reducers and increasers. Tees

Tees (Figure 9-46) connect branches to continuous lines. A test tee is used in stack and waste installations where the vertical stack joins the horizontal sanitary sewer. It allows the plumber to fill the system with water while testing for leakage. A tapped tee is used with the venting system where it is called the main vent tee. The sanitary tee is commonly used in a main stack to allow the takeoff of a pipe branch.


Figure 9-46 — Typical sanitary pipe fittings - Tees. Ninety-Degree Y-Branches
 (Figure 9-47)

Straight 90° Y-branch—feeds a branch into a main as nearly as possible in a line parallel to the main flow. Reducing 90° Y-branch—same as straight type except the branch is smaller than the main. Double 90° Y-branch (or double combination Y and 1/8 bend)— especially useful as an individual vent. Box type 90° Y-branch—two takeoffs form a 90° angle with the main pipe and also spaced 90º from each other. Figure 9-47 — Typical sanitary pipe fittings – 90º Y-Branches. Forty-Five-Degree Y-Branches

45° branches (Figure 9-48) join two or three sanitary sewer branches at a 45° angle in a straight-Y, double-Y or V configuration. Straight 45° Y-branch—true Y. Reducing 45º Y-branch—a straight section with a 45° takeoff of a smaller size Figure 9-48 — Typical sanitary pipe fittings – 45º Y-Branches.  9-26 Vitrified clay pipes and concrete pipes are used outside of buildings, which greatly reduces the number of different types of necessary fittings.

1.2.3 Joints and Connections

A sanitary drainage system’s joints and connections will vary according to the type of pipe material used. Lead and Oakum Joint,

Compression Joint, and No-Hub Joint Cast-iron soil pipe uses one of three types of connections. (Figure 9-49) Lead and oakum joint—oakum (made of hemp impregnated with bituminous compound and loosely twisted or spun into a rope or yarn) packed into the hub completely around the joint, with melted lead poured over it. Compression joint—an assembly tool forces the spigot end of the pipe or fitting into the lubricated gasket inside the hub. No-hub joint—a gasket with a stainless steel shield and retaining assembly to tighten as a clamp. Figure 9-49 — CISP joint connections. Mortar and Bituminous Joints

Common to vitrified clay or concrete pipes and fittings, following an oakum packing, instead of lead, joints are mortared using grout (a mixture of cement, sand, and water). Speed seal joints (rubber rings) (Figure 9- 50) have become widespread in joining vitrified clay pipe. They eliminate the oakum and mortar joints thus expediting project completion and lowering labor costs. This type of seal is made a part of the vitrified pipe joint when manufactured. Figure 9-50 — VCP speed seal.

1.2.4 Traps

A trap (Figure 9-51) is a device that catches and holds a quantity of water, thus forming a fluid seal that prevents sewage decomposition gases from entering the building through the drainage pipe. A number of different types of traps are available; however, the trap mainly used with plumbing fixtures is the P-trap.

Figure 9-51 — Typical P-trap.

1.2.5 Vents

Without a vent, water or waste discharged from one fixture tends to create a vacuum/siphon affect on other fixture traps as it goes through the pipes. A properly functioning vent (pipe) (Figure 9-52) allows sufficient air to enter the system to eliminate that condition. It also directs gasses that develop naturally in a sewage drainage system to vent to the outside. This means that the vent piping system must serve all the various fixtures. It does this by connecting a main vent (with branches) to the main soil and waste vent at a location below the lowest and above the highest waste connection. Vent piping materials may be galvanized pipe, cast-iron soil pipe, and, at times, brass, or copper, but plastic piping is increasingly the material of choice. A main vent is the principal artery of the venting system. Vent branches connect and run undiminished in size as directly as possible from the building drain to the open air above The main soil and waste vent is that portion of the main soil and waste stack that extends above the highest fixture branch through the roof to the exterior of the building. Figure 9-52 — Typical main vent system.  9-29 Installers use various configurations to vent fixtures. The selection depends largely on the location and grouping of the plumbing fixtures. The individual vent (Figure 9-53) (also referred to as a back vent or continuous vent) is the most common. This vent can be adapted to all fixtures and installed as a single or a battery of two or more. It prevents both direct and indirect siphonage. A common vent (Figure 9-54) vents two traps to a single vent pipe when lavatory pairs are side-by-side, or back-to-back on either side of a partition. The waste from both discharges into a double sanitary tee. Figure 9-54 — Common vent. Figure 9-53 — Individual vent system in single and battery.  9-30 A circuit vent (Figure 9-55) extends from the main vent to a connection on the horizontal waste branch between the next to last and last fixtures with a maximum of eight fixtures on any circuit. Since some fixtures discharge their waste through a part of the pipe that acts as a vent for others, the vent may clog. To reduce clogging, the vent should connect to the top of the branch rather than the side. Water and waste from the last fixture scours the vents of the other fixtures. Figure 9-55 — Circuit vent. When liquid waste flows through a portion of a vent pipe, it is a wet vent. (Figure 9-56) A loop vent also has liquid waste through a portion and then connects into the waste stack unit to form a loop. Useable for a small group of bathroom fixtures, such as a lavatory, water closet, and shower, it needs to be sized to accommodate those three units. A lavatory should be individually vented to prevent loss of the trap seal through siphonage and allow the relatively clean water to scour the wet vent to prevent a buildup of excessive waste material. Figure 9-56 — Wet vent and loop vent. NOTE A water closet must not drain into a wet vent. Proper-sized piping must be used in all phases of the venting system. The diameter of the main vent stack must be no less than 2 in. when draining more than four units. The actual diameter depends on the developed length of the vent stack and on the number of fixture units installed on the soil or waste stack. The diameter of a vent stack should be at least as large as that of the soil or waste stack. 

1.2.6 Branches

Soil and waste pipe branches (Figure 9-57) are horizontal branch takeoffs that connect various fixtures and the vertical stack Installers can use a Y-branch with a 1/8 bend caulked into it, or a sanitary tee, an extra-shortpattern 90º Y-branch. The sanitary tee is better to eliminate the extra fitting and caulked joint required for the 1/8 bend takeoff but some local codes allow additional 1/8 bend connections. Generally, waste pipes have a downward grade to ensure complete drainage. Horizontal vents should also pitch slightly downward to facilitate discharge of condensation. Figure 9-57 — Typical branch connections.


Test Your Knowledge

1. Builders commonly use copper, plastic, galvanized steel, or cast iron. Of those, plastic is becoming the most common for use due its _______ and _________________.

A. strength, lack of friction
B. chemical properties, lower cost of materials
C. lower cost of materials, ease of installation
D. durability, availability

In this lesson, a mechanical plan refers to drawings, layouts, diagrams, and notes that relate to water distribution and sanitary drainage systems only. Heating and air conditioning, refrigeration, and other like systems are not included.

- To Table of Contents -


2.1.0 Water Supply and Distribution Diagram

Normally, a structure’s water supply system starts at the water main. A self-tapping tool (Figure 9-58) drills and taps into this source (the source is still under pressure) and a corporation stop is installed during the same process.


Figure 9-58 — Water main self-tapping tool and typical service line.

Water then enters the building through a coldwater service line that usually runs through a gate valve-meter-gate valve configuration.

As an engineering technician, you may be called upon to develop field sketches and drawings from larger sets of plans, or in reverse, to do “as-built” drawings and sketches. You may at some point need to do drawings of existing conditions so planners involved in a remodel or rehabilitation project can design retrofit potential possibilities. The following three isometric diagrams demonstrate typical layout drawings that apply to mechanical systems for plumbing, that is, for water distribution and soil and waste removal.

Figure 9-59 shows typical hot- and cold-water service lines for a single-story residential building and how the lines connect to the fixtures. This layout is a riser diagram in isometric as a method of visualizing or showing a three dimensional picture of the pipes in one drawing.


Figure 9-59 — Typical hot-water and cold-water risers diagram.

2.2.0 Waste and Soil Drainage Diagram

Figure 9-60 shows the waste and soil pipes fittings and symbols associated with the hot- and cold-water risers diagram. The arrow represents the direction of flow; all pipes are sloping towards the building drain.


Figure 9-60 — Typical waste and soil risers diagram.

Figure 9-61 shows the basic layout of a simple but typical drainage system. Refer to it as the lesson presents the function of each element.


Figure 9-61 — Basic drainage system layout and terminology.

2.3.0 Plumbing Layout

In construction drafting, a mechanical (or utility) plan normally includes both water distribution and sanitary drainage systems combined, especially on smaller buildings or houses. The plumbing layout is usually drawn into a copy of the floor plan for proper orientation with existing plumbing fixtures, walls and partition outlines, and other utility features. Figure 9-62 shows a typical plumbing layout. For mechanical symbols, refer to ANSI Y32.4-1977, Graphic Symbols Used in Architectural and Building Construction.


Figure 9-62 — Typical plumbing layout plan.

2.4.0 Mechanical Symbols

As previously stated, you are not expected to design a system, but you will be expected to draw a workable plumbing plan for use by the plumbing crew or any other interested parties. To accomplish this, you must be familiar with terms, symbols, definitions, and basic concepts of the plumbing trade. As a rule, plumbing plans show the location of fixtures and fittings to be installed, along with the size and route of piping. The details are left to the plumber (UT), who is responsible for installing a properly connected system according to applicable codes, specifications, and good plumbing and construction practices. Generally, plumbing plans make use of four types of symbols: piping, fittings, valves, and fixtures.

2.4.1 Piping Symbols

On plans, line symbols for piping are solid or dashed lines indicating type, location, and proposed use. (Figure 9-63) Size should be noted alongside each route.


Figure 9-63 — Line symbols for piping.

Piping up to 12 in. in diameter is referred to by its nominal size, approximately the inside diameter (I.D.). The exact inside diameter depends on the classification of pipe. Heavy types of piping have smaller inside diameters because their wall thickness is greater. Piping over 12 in. in diameter is referred to by its outside diameter (O.D.).

2.4.2 Fitting Symbols

The pipe fitting symbols shown in Figure 9-64 are the basic line symbols used in conjunction with valve symbols. They define the size of the pipe, the method of branching and coupling, and the purpose of the pipe. This is important because the purpose of the pipe determines what piping material to use. The inverse is also true; the piping material will determine how it can be used. 


 Figure 9-64 — Fitting symbols for piping.

Only a few of the symbols for fittings, joints, and connections are shown here. For additional symbols on welded and soldered joints, refer ANSI Y32.4-1977, Graphic Symbols Used in Architectural and Building Construction.

2.4.3 Valve Symbols

Figure 9-65 shows symbols used for only the most frequently encountered valves. Normally, type of material and valve sizes are not identified on mechanical drawings but are assumed from the type of material and size of connecting pipe. However, when specified on the lists of materials (plumbing takeoff), valves are called out by size, type of material, and working pressure; for example, 2-in. gate valve, PVC, 175-lb working pressure.


Figure 9-65 — Valve symbols for piping.

2.4.4 Fixture Symbols

Figure 9-66 provides symbols and abbreviations for general appurtenances such as drains, as well as other basic fixtures such as baths, sinks, and water closets. The latter are often shown on the plans by pictorial or block symbols. The extent to which the symbols are used depends on the nature of the drawing. In some cases, fixtures are specified on a bill of materials or other schedule keyed to the plumbing plan. When the fixtures are identified on a schedule, you can use symbols that closely resemble the actual fixtures or obtain commercially available mechanical symbol templates.


Figure 9-66 — Plumbing fixture symbols.



As an engineering technician, you must have wide familiarity with all the construction disciplines, their general terms, materials, equipment, and procedures, to be able to translate drawings into working sketches or the reverse, field sketches into drawings. Mechanical systems for water distribution and waste removal are only two of many, but they are also two of the most common. A comfortable knowledge of plumbing terminology (Figure 9-67), materials, and symbols will expedite any tasking you may have to produce their drawings.


Figure 9-67 — Typical water supply terminology.


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Review Questions

1. The system of pipes, fixtures, and appurtenances used inside a building for supplying water and removing wastes is known by what general term? A. Mechanical systems B. Plumbing C. Water distribution D. Piping 2. With which of the following codes must you become familiar when working with mechanical plans? A. National Plumbing Code and National Electrical Code® B. National Plumbing Code and local NAVFAC codes C. Local codes and National Plumbing Code D. Local codes and ANSI codes 3. A water service pipe begins at the _______________. A. hose bib B. water main C. water meter D. water distribution pipe 4. A water distribution pipe begins at the _____________. A. hose bib B. water main C. water meter D. water service pipe 5. Traditionally, copper has been widely used for tubing in piping systems for which of the following reasons? A. It is less costly than other types of pipe. B. It is available in two wall thicknesses and is faster to install. C. It does not rust and is resistant to scale particles in the pipe. D. Fittings are screwed to the pipe which allows for faster completion of the piping system. 6. Copper pipe is manufactured in ___ grades and thicknesses, ___ of which are appropriate for water distribution systems from water main to tap. A. 6, 3 B. 5, 3 C. 4, 2 D. 4, 3  9-41 7. Copper is durable and connects well to valves but should not be installed if the water has a ____________level. A. low-pH (high acidic) B. high-pH (low acidic) C. high water table D. low water table 8. Which of the following types of copper tubing is frequently used as replacement piping because of its flexibility? A. Type K B. Type L, hard tempered C. Type M D. Type L, soft tempered 9. Which of the following advantages does plastic pipe have over metal? A. Flexibility B. High resistance to rupture and total resistance to rust C. It can be installed either above or below ground D. All of the above 10. What type of polyvinyl chloride pipe can be used in both cold-water and hot-water systems? A. PVC B. APVC C. CPVC D. PVC-C 11. The principal mechanical difference between CPVC and PVC is that CPVC is significantly more malleable, allowing greater flexibility and ________________. A. long runs B. crush resistance C. quick connections D. lighter handling 12. Galvanized steel pipe sizes are based on what nominal size? A. Inside diameter B. Outside diameter C. Wall thickness D. Inside radius  9-42 13. What type of pipe material is frequently used for water mains and service pipe up to a building? A. Galvanized steel B. Copper C. Cast-iron D. Plastic 14. What two types of malleable iron or cast iron pipe fittings are used for steel pipe or wrought iron? A. a) pressure, b) recessed B. a) nominal, b) sized C. a) inside diameter, b) outside diameter D. a) nominal, b) recessed 15. A Durham fitting is also known as a ____________ fitting. A. standard B. pressure C. cast-iron drainage D. speed 16. How many parts does a ground joint union have? A. 1 B. 2 C. 3 D. 4 17. How many parts does a flange union have? A. 1 B. 2 C. 3 D. 4 18. An eccentric reducer joins pipes of different sizes so the two pieces of pipe will ___________. A. line up for a straight run B. turn at right angles C. turn vertically for a riser D. not be in line with each other 19. A nipple is a ____________________. A. cast-iron threaded cap B. galvanized threaded plug C. length of pipe with a male thread on each end D. copper reducing coupler  9-43 20. What type of fitting for joining straight should be used in runs of dissimilar metal pipe that require easy disconnection? A. Union B. Coupling C. Dielectric union D. Dielectric coupling 21. What type of piping uses flared and sweated joints? A. Plastic B. Copper C. Cast-iron D. Galvanized steel 22. What type of piping uses solvent welded, fusion welded, fillet welded, threaded, and flanged joints? A. Plastic B. Copper C. Cast-iron D. Galvanized steel 23. What type of piping uses bell-and-spigot, and mechanical joints? A. Plastic B. Copper C. Cast-iron D. Galvanized steel 24. What type of piping uses threaded joints only? A. Plastic B. Copper C. Cast-iron D. Galvanized steel IN ANSWERING QUESTIONS 25 THROUGH 28, SELECT THE TYPE OF VALVE FROM THE FOLLOWING LIST THAT BEST MATCHES THE DESCRIPTION GIVEN IN THE QUESTION. A. Globe Valve B. Gate Valve C. Check Valve 25. This valve has a wedge-shaped, movable plug or round disk that fits tightly against the seat when closed. A. A B. B C. C  9-44 26. This valve is well suited for use when a regulated flow is required. A. A B. B C. C 27. This valve must be operated in the fully open or fully closed position. A. A B. B C. C 28. This valve is used to prevent backflow in a pipeline. A. A B. B C. C 29. Any pipe ______________________ must be adequately supported to prevent sagging. A. from the water main to the meter B. from the meter to the distribution pipes C. aboveground or in the building interior D. corporation stop to the building 30. On water mains, thrust blocks should be installed for what purpose? A. To prevent pipe displacement caused by high water pressure B. To prevent pipe ruptures caused by high water pressure C. To prevent sagging due to the weight of the piping material D. To prevent sagging due to the weight of the pipe and the water contained in the pipe 31. What purpose does pipe insulation serve? A. Helps prevents heat passage from pipes to surrounding air B. Helps prevent lines from absorbing heat C. Subdues noise D. All of the above 32. Where is cast-iron soil pipe (CISP) normally used? A. Where the soil is unstable B. Under buildings C. In soil containing cinder and ashes D. In light traffic areas  9-45 33. Vitrified Clay Pipe (VCP) is made of _______________. A. vitrified crushed rock B. moistened powdered clay C. vitrified glass D. moistened powdered silica 34. Which piping material is becoming increasingly popular for use in underground sanitary sewage systems? A. Cast iron B. Polyvinyl chloride C. Concrete D. Wrought iron 35. What cast-iron fitting should you use to make a 22 l/2-degree change in pipe direction? A. Combination Y and 1/8 bend B. 1/4 bend C. Short sweep 1/4 bend D. 1/16 bend 36. A test tee is used in stack and waste installations where the vertical stack joins the ________. A. horizontal sanitary sewer B. vent stack C. clean out D. double Y branch 37. Which of the following type of joint is not used for cast-iron soil pipe? A. Speed seal B. Compression C. No-hub D. Lead and oakum 38. What fittings are used in waste pipe systems to catch and hold water, thereby forming a seal to prevent sewer gases from backing up into a building? A. Traps B. Street ells C. Valves D Vents  9-46 39. Without a vent, water or waste discharged through a system tends to create a ________ effect on other fixtures. A. pressure B. siphon C. overflow D. venting 40. When liquid waste flows through a portion of a vent pipe, _________. A. it is plumbed incorrectly B. it will block the venting C. it is a wet vent D. it is a temporary overflow 41. What type of configuration does a building’s cold water service usually run through? A. Globe valve-gate valve-meter B. Gate valve-check valve-meter C. Gate valve-meter-globe valve D. Gate valve-meter-gate valve 42. In what way, if any, do waste stacks differ from soil stacks? A. Waste stacks carry human waste, soil stacks do not B. Soil stacks carry human waste, waste stacks do not C. Waste stacks empty into building drains, soil stacks empty into building sewers D. None 43. Unless designated otherwise by local code, what is the minimum distance a building drain must extend beyond the building wall? A. 2 ft B. 3 ft C. 6 ft D. 10 ft 44. Piping up to 12 in. in diameter is referred to by its ______________. A. inside diameter B. nominal size C. outside diameter D. fitting size 45. Piping over 12 in. in diameter is referred to by its ______________. A. inside diameter B. nominal size C. outside diameter D. fitting size  9-47 46  For valve symbols, the type of material and valve size should always be identified on the drawings. A. True B. False