n this first of two installments on the subject of DWV (drain-waste-vent) materials, we’ll lead off with a general look at the functions and requirements of components of such systems. Following this, we’ll move into the specific details of the cast iron variety. As a logical place to start, let’s review what we said about the role of DWV in our introductory coverage of the residential plumbing system (Section I, “The Big Picture.”)

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"This section is the first of a two-part coverage of drain-waste-vent (DWV) systems and their components, with a specific examination of cast iron soil pipe and fittings."

The DWV system in a house or building is intended to remove waste water and accompanying solids from the points of water usage. Unlike supply systems, however, the transmitting of such wastes is not accomplished through pressure. Instead, the system relies entirely on gravity to do the job. While this may seem simple in some respects, the overall design of the system and its components is far more complex than most people would imagine. As we explained in the first section, the venting requirements of the system require a careful piping layout in order to assure the maintaining of atmospheric pressure in all areas (and thus prevent the unwanted siphoning of water from the traps).

Another key factor in the overall system design is the matter of proper pitch of lines to facilitate the movement of waste water and solids. On horizontal runs, this pitch must be rather precise. If the line is not pitched enough, the overall flow will be retarded. If the line is pitched too much, water could drain too rapidly, leaving accompanying wastes stranded.

The design of the system is not the only significant aspect; equally important are certain considerations in regard to the DWV pipe and fittings components used:

Corrosion Resistance: Since there is more than just water being transmitted through drainage systems, the ability of the piping materials to resist corrosion is of greater concern than with supply piping. Human wastes, food wastes and chemicals (especially drain-cleaning types) are all common to the residential system, and it is important that only those materials be used that can resist attack from these wastes.

Noise Insulation: While you normally think of restricted supply lines as the culprits in causing noisy plumbing, DWV systems can also give off unwanted signals of usage. Each basic type of DWV piping material has a different characteristic in this respect, and if the system’s sound level in a house or building is a critical concern, this factor should be closely examined.

Capacity: Just as an undersized supply system can result in water delivery that is too slow (and often noisy), an undersized drainage system results in water that drains too slowly—and may have a tendency to clog and/or back up. On the other hand, piping that is oversized for a particular application runs the hazard of inadequate transmission of solids.

Unobstructed Joints & Gentle Bends: If there are often solids in the waste water of a DWV system, and our only means of movement is gravity, this necessarily means that the system needs all the help we can give it to facilitate free flow. For this reason, DWV systems use fittings that differ significantly from supply fittings.

First of all, DWV fittings are designed with unobstructed passage in relation to the mating pipe sections. While supply fittings typically create a step between the inside diameters of the pipe and fitting, such a relationship would be undesirable in use with DWV systems, since solids would tend to catch on the protruding shoulder of the down-stream pipe end.

In addition, DWV fittings always avoid sharp turns internally, to prevent solids from hanging up in the bend.A good comparative example of this is the tee configuration used with supply systems, and the type used with DWV. Whereas the supply tee branches off on an abrupt angle internally, the DWV version (called a “sanitary tee”) has a more gently curved internal passageway.

Local Code Requirements: All of these factors aside, you can’t install any DWV materials that are not specifically approved by the code-governing agency in each area. Admittedly, the determinations of such approving agencies are not always made on the basis of purely objective considerations, but that’s a whole different story we won’t dig into here. Simply be aware that you have to deal with the realities of what is and isn’t approved in your area.

In residential plumbing systems today, there are three basic types of DWV piping materials that are commonly used: cast iron, copper, and plastic (usually ABS or PVC). (In the commercial/industrial field, there are other materials frequently used, and we’ll save that

The term “cast iron soil pipe” is to DWV systems what “Kleenex” is to tissues, and “Scotch Tape” is to cellophane tape. In other words, cast iron is so closely associated with the DWV application, it means just about the same thing in many people’sminds.Years ago this was fine, since cast iron was just about the only material used for such systems. But things have changed.Today, if you say that cast iron soil pipe is DWV material, you’d be correct; but conversely, if you say that DWV is the same thing as cast iron soil pipe, then you’re getting off the track.

As already stated, there are three basic materials commonly used in residential DWV systems today, only one of which is cast iron. There is a tendency for some industry people to use “soil pipe” as a generic substitute for DWV, and that’s where the confusion arises. Traditionally, the term “soil pipe” has been used handin-hand with cast iron, and in common practice, is not used in reference to other DWV materials.

In other words, rather than being called “plastic soil pipe,” the plastic equivalent is most often referred to as “plastic (by specific name) DWV pipe and/or fittings.” Technically, two of the engineering societies allow the use of the term “soil pipe” with other DWV materials, but in reality, the trade doesn’t seem to go along with that thinking.

With its long history of successful use in drainage systems (both DWV and storm water applications), you can safely assume that cast iron has a number of strong points to its credit. Manufacturers of this material point out the following advantages of their products:

1. resistance to corrosion, chemical attack and abrasion;
2. resistance to piercing;
3. resistance to crushing (important in underground installations);
4. quiet, sound-insulating service;
5. versatility of joining methods.

Cast iron is one of the most widely used materials in American industry today. The type employed in the manufacture of soil pipe and fittings is specifically identified as “gray iron,” which is selected for its superior strength, corrosion resistance and moldability.

As the name says, cast iron soil pipe is created by a casting process, which is another name for “molding.” Unlike most metal supply piping materials, which are formed from existing shapes of material (flat strips and billets, for example), soil pipe isformed by pouring molten iron into a mold. As the iron cools, it solidifies into a hard, precisely formed shape.

A more recent advancement in such manufacturing has been the development of a molding process called “centrifugal casting.”With this approach, the mold is spun at a high speed while the molten metal is introduced. The action forces the material into an even distribution around the entire circumference and length of the mold surface, providing a precisely defined configuration without need of a center core pin. All soil pipe manufacturers now use this centrifugal casting process.

Cast iron soil pipe fittings, on the other hand, use the more traditional “static” casting methods. In this case, you typically have a two-part mold consisting of female configurations formed into a hardened sand composition. Internal passageways are made possible by suspending a core component of the mold between the two basic halves.The molten metal is then poured into the pattern, where it cools and hardens. The sand surrounding the mold and core is then broken away, leaving the newly formed fitting.

Two Basic Types Of Soil Pipe: Just as the term “DWV” isn’t as simple as it once was, even soil pipe itself has come to mean more than just one thing.There are now two basic types of soil pipe (see drawing), based on the systems of installation involved:

• Hub-And-Spigot Type: This is the original configuration of soil pipe, still used today. Unlike supply piping materials, that are “male” on both ends, hub-and-spigot soil pipe is designed with a male provision on one end, and a female one on the other. Accordingly, fittings used with this system of piping are designed with appropriate male-female connections. Straight sections of this material are assembled by inserting male ends directly into female ends.
• No-Hub Type: A more recent development in the industry, the nohub type of soil pipe is designed with a male configuration on both ends. In other words, instead of a “hub-andspigot,” you have a “spigot and spigot.” Assembly in this case is accomplished by means of external coupling—typically a stainless steel or cast iron clamping arrangement.

In practice, there is a tendency for people in the trade to identify only the no-hub variety of soil pipe in specific terms. In other words, if only the term “soil pipe” is used, it is often assumed that the traditional hub-andspigot type is meant. But if “no-hub soil pipe” is intended, it is specifically stated that way. If everybody understands that system of communication—fine. But frankly, we feel it’s

Cutting: As with any type of piping material, it is frequently necessary to cut cast iron soil pipe to length in order to make up a given run. There are various means of accomplishing this.

The simplest approach is to scribe a groove around the pipe at the desired location with a hacksaw or chisel, then tap the pipe to fracture it there (cast iron, being relatively brittle, will break cleanly when scored properly). Most contractors of any size will use a more refined piece of equipment for this operation, however.The basic cutting device is a chain with small cutters, that is fastened around the pipe. This is gradually tightened by means of aratchet lever or hydraulic pump, until the pipe fractures from the biting of th e cutters.

Hub-And-Spigot Assembly: In this category, there are two alternate means of making connections: the “compression” joint (newer and now more widely used), and the traditional “lead-and-oakum” method.

1. Compression Gasket Method: This system utilizes a sleeve-like rubber gasket as the means to seal and mechanically attach the mating ends of soil pipe. With this system, the male end of the mating pipe is plain (no beaded spigot configuration) for easy insertion.
   
   The assembly of the two pipes together causes the rubber material to displace into the undercut groove inside the surface of the hub, locking the components in place. It is often necessary to use a lubricant to accomplish this, and in some cases, a special lever-like device is used to draw the two sections of pipe together.
   
   
2. Lead-and-Oakum Method: This alternate approach uses two basic ingredients to provide sealing and attachment. First, the oakum is packed down into the recess with a special tool. Oakum is a rope-like material typically made of hemp fibers, impregnated with either oil or a powdery substance.
   
   Exposed to water, oakum tends to swell, tightly filling the cavity into which it is packed.To form the top side of this cavity, hot, molten lead is poured on top of the oakum, which then coolsinto a solid retaining ring. The lead is locked into position by the undercut groove of the hub.
   
   
3. No-Hub Assembly: The two key components in joining this type of soil pipe are the rubber sleeve and the clamping device. The most common type of clamp used is made of acorrugated stainless steel collar, with worm-gear tightening bands at either end. (Largersizes require the use of two tightening bands at either end.) The corrugated collartightly grips the rubber and assures even distribution of compression exerted by the tightening bands. (See the illustration on the next page for further clarification.)
   
   There is an alternate system available for use with no-hub soil pipe that assembles by bolting two halves

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   of a cast iron collar over a rubber sleeve.

Theoretically, hub-and-spigot soil pipe is available in two weight classes: Service Class (SV) and Extra Heavy (XH). In practice, however, few manufacturers continue to produce the extra heavy grade today. Modern foundry technology, particularly the centrifugal casting processes, now provides service weight soil pipe that is superior to the old extra heavy class pipe (made with static processes).

No-hub soil pipe is available in just one grade, about the same in wall thickness as the service class of the hub-and-spigot type.

Though local codes vary, as a rule, no-hub soil pipe is used above ground, whereas service

Because there are two basic types of soil pipe based on the systems of connection involved, there are necessarily two types of fitting systems used with them. Predictably, hub-and-spigot soil pipe uses fittings that also have mating hubs and spigots. And accordingly, no-hub soil pipe uses fittings that have no hubs.

The material we covered in Section IV on supply pipe fittings a few pages ago will be a good foundation for this portion of the article. If you grasped that, then you should be able to understand how those same basic concepts apply to fittings used with DWV systems.

Many people are puzzled when they see the maze of different fittings produced for use in this area. Why all the subtle variations and funny combinations? There are several reasons for this:

1. Angles in DWV piping must be gradual to prevent the clogging of solids. Locations of branch junctions are critical in respect to the maintaining of proper venting.
2. Since the material is harder to work with than supply piping, it is desirable to use multi-function fittings whenever possible.
3. In presenting the specific fittings available in this product area, we will use an outline based on function, similar to the one we used with supply fittings in our last section.

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• Bends: What you normally think of as an “elbow” in the case of supply fittings is called a “bend” in a soil pipe system. But it’s not as simple as just that. While elbows come in two common angled configurations—90° and 45°, bends are available in five different angles. And instead of designating these variations by degrees-of-angle, they are specified by fractions of a full circle.Thus, when we refer to a “1/4 bend” fitting, we mean that its angle represents 1/4 of 360° (90°). Other bends are available in 1/5, 1/6, 1/8 and 1/16.
  1. Long Bends: To save as many cutting and assembling steps as possible, bends are also available with extended spigot ends. Sizing for these is designated as a compound number, such as 4 x 12. This would mean that the fitting is intended for 6 use with 4” soil pipe, with a distance of 12” from the end of the spigot to the center line of the radius.
  2. Short & Long Sweeps: A sweep is a fitting that makes a 90° angle more gradually than a coresponding bend. As you might guess, a long sweep turns the corner even more gradually than a short one. As a comparative example, using 2” sizing, a conventional 1/4 bend makes the turn with a radius of 3”, while a short sweep does it with a radius of 5”, and a long sweep stretches the turn out to a radius of 8”.
  3. Closet Bends: Much like a 1/4 bend in basic configuration, a closet bend is used to connect to the mounting flange of a water closet. Typically, closet bends are designated with “double” or “triple” numbers. The first numbers are diameter (regular and reducing sizes), next is the height of the fitting from the center line of

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     the radius, and last is the length of horizontal run.

• Sanitary Tees: In basic function, this is similar to the tee used with supply piping, with one important difference. The internal configuration is this case is specially formed to provide a gradual, sweeping angle, as opposed to the rather abrupt turn characteristic of the supply type.
• Vent Tees: Just so we can immediately contradict ourselves, here’s an exception to the rule we just made. When a tee is used in a nonwater portion of a hub-and-spigot system (in other words, serving strictly a vent function), a tee with a conventional configuration may be used. Since these deal with the movement of just air, they do have more abrupt angular passages. (With no-hub systems, sanitary tees are used for both functions.)
• Wyes: Since the branch in this case enters the fitting at a more gradual angle (45°), it does not require an internal design much different from its supply fitting counterpart.
• Sanitary Crosses: Like the sanitary tee, this fitting is designed with sweeping internal angles to facilitate the free flow of wastes without hanging up. The sanitary cross

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  permits the joining of two branch lines into a main drainage run.

By now, we know what a reducer is, but what’s an “increaser”? It’s really the same basic configuration as the reducer, the main difference being the application involved. In northern climates, increasers are used on the top of vent stacks above the roof line. The increased diameter of the stack is necessary to prevent frost build-up on the inside that might obstruct or even close off the passageway (moisture in the rising vapors condenses into frost on the cold inside surface at that point).

Occasionally, in order to clear an obstacle, it is necessary to use a special fitting called an “offset.” This is also referred to as a “1/8 bend offset,” though it is important to understand that it does not change the basic direction of the drainage or vent run—it simply offsets the run in a parallel fashion.

Offsets are identified with a compound number to designate the basic size of the fitting, and the distance of the offset from center line to center line. As an example, a “4 x 10 offset” would be a fitting used with 4” soil pipe that has a dimension of 10” from the center line of one end to the center line of the other end. (Incidentally, the term “1/8 bend offset” is based on the fact that the configuration is formed through the use of two

Though many of the trap requirements of a house or building are met through the use of other materials at the point of outlet on the individual fixtures involved, there are certain situations that require a trap to be an integral part of a DWV system. Floor drains are a good example of this. In order to maintain a protective water seal below the opening of floor drains, it is necessary to provide a trap configuration in the drainage line leading away from such points. In addition, traps are located at some point in building drains to prevent gasses from connecting sewers or septic systems from backing into the DWV system of the building.

The common configurations of soil pipe traps are the “P” trap, the “S” trap, and the “running trap.”

In cases where it is necessary to use both hub-and-spigot and no-hub soil pipe in the same overall system, there are transition fittings that can be used to join the two. As you might guess, such a configuration consists of a hub at one end, and a no-hub type of

All DWV systems must have the provision for being opened at strategic locations to clean out clogs in the line. These access areas are usually provided by means of a wye fitting that closes off the branch opening with a plug.Typically, a plug is a threaded piece that screws

In case you are thinking that you now know every conceivable configuration of soil pipe fitting made, don’t get too excited—you’ve just started. The coverage up to this point has provided an overall picture of the most basic configurations. From here, you have to be aware that there are countless variations and combinations of functions designed into many different types of individual fittings.

As a common example, many of the basic types we have just covered have provision for what is called a “side opening.” Take the simple 1/4 bend as an example. A particular DWV system design may call for the joining of a branch drainage line to a main one at the point of that bend. Thus, provision is made for this through an opening in the side of the fitting.

There are also fittings that allow for two such branches to intersect a fitting.These are designated as having “right and left” inlets. In addition, there are other combinations of functions and connections available in single “hybrid” fitting designs. An example of this is the “wye” with a 1/8 bend on the branch inlet. There are also fittings that add a reducing function to a basic configuration. Certain others make provision for a threaded connection from a waste or vent line.

Because of all these possible variations, it is extremely important to clarify every aspect of the fitting in question. Always determine these factors:

1. What is the basic soil pipe system (hub-and-spigot or no-hub)?
2. What is the basic size of the fitting (dimension of main run with which it is being used)?
3. What is the size of the branch(es), if any?
4. What is the location of side inlets, if any (right, left or right-andleft)?
5. What is the diameter of side inlets, if any?
6. What is the type of connection for each opening (hub, spigot, tapped [threaded] )?

Generally, hub-and-spigot fittings that are used for branch connection functions (tees,wyes, crosses) will give the dimensional identification in the following order:

1. Spigot on main (“main” refers to the direction of the main pipe run involved);
2. Hub on main;
3. Hub on branch;
4. Hub on second branch (if applicable).

For example, a wye specified as 4 x 4 x 2, has 4” connections at both spigot and hub in the