PVC pipe

[zelmo]

Can someone explain why PVC is allowed to be used to supply water to a house, but not for distribution inside? (At least in some municipalities.)

[LazyPup]

When PVC was first introduced into the plumbing trade it was used very extensively, however it was soon learned that PVC has a very high failure rate when water temperatures exceed 100degF. For a short time some plumbing codes were amended to allow PVC for cold water service but not for hot water. This lead to a lot of confusion and improper use, therefore the obvious solution was to discontinue PVC pipe in the Distribution system.

PVC also becomes very brittle when continuously exposed to sunlight, thus it works ok underground but tends to have a high failure rate when used above grade.

The codes now allow PVC schedule 40 which bears ASTM 1785 label as suitable for "SUPPLY" and underground service outside of the structure, such as for lawn irrigation purposes but it may not be run under a slab or inside the confines of a structure.

Schedule 40 PVC with the ASTM 2665 label may be used for all DWV (Drain, waste & Vent) systems.

Some PVC pipe currently sold in the local hardware or home supply stores carries both the ASTM 1785 & the ASTM 2665 label.

When selecting PVC pipe you must be very careful to check the ASTM listing number. If you happen to use PVC pressure pipe (ASTM 1785) in place of Drain, Waste & Vent pipe (ASTM 2665) an inspector may red tag the job and require it be changed out. Also, most home inspectors check this very carefully and improper use of PVC can lead to serious problems when selling a home.

[zelmo]

Thank you for the explanation. I hope you don’t mind but I need to know a little more because I am using PVC for an aquarium application and code isn’t the issue. Toxicity and structural integrity are my concerns.

I need to run water through a two foot section of 2 inch diameter PVC. Vinyl hose is attached to each end so there is no stress. Pressure is limited to whatever it takes to pump water to rise 5 feet and empty into the tank. Temperature is 86 degrees and it is located where it will not see sunlight.

My local stores only carry DWV pipe. The one that will cut 2 feet only has Cresline coextruded cellular core PVC DWV, IPS shc40, ASTM F 891 04.. Do you think I will have any problems with this?

[kactuskid]

This is a very educational thread and you got my curiostiy up now LazyPup. You say that an inspector would redtag an installation using the Pressure type PVC inplace of the Drain type. I would think the pressure type would be stronger and well suited for use in a drain application. And I could see where you wouldn't want the drain type used for pressure applications. So, why would it not be approved to use the pressure type for a drain waste vent application? Thanks.

[LazyPup]

Zelme

For your application PVC DWV grade should work fine..there are no issues of toxicity.

For the record the vertical static head weight of water is ".434lbs/vertical foot" therefore the pressure required for a 5 ft rise would be .434 x 5 = 2.17psi

Although it is not commonly known, Clear PVC pipe and fittings are available by special order and they are often used in industrial or food production facilities that were previously constructed with glass pipe. I once saw a house that was completely plumbed, both supply and DWV with clear pipe. It was very interesting to see the flow of liquids through the pipe and it certainly made finding clogs in the drain system much easier.

Kactuskid:

Technically there is a difference in the internal cell foam construction between the two types of pipe and the two grades are made to different ASTM standards, however most of the Pressure pipe commonly sold in local hardware or homesupply centers will meet both standards and is listed on the pipe as approved for both ASTM1785 & ASTM2665. Some of the pipe that is only listed under ASTM2665 will also bear the index DWV on the pipe wall.

It is very important when running PVC pipe that the pipe be installed in such a manner that the writing on the pipe wall is clearly visible for inspection.

There were many homes plumbed with PVC during the short period that it was approved and if you have a PVC system you may continue to use PVC for maintenance however,sSome people make the mistake of using the primer to erase the writing off the pipe wall for appearance sake. Absolutely do not do that because an inspector would surely reject it if the writing is not visible.

WE must also understand the official definition of "Maintenance" versus "New construction". Maintenance is the act of maintaining an existing system in exactly the same manner as it was originally installed. Any changes to the original design or layout constitute "New Construction" and could require permits, inspections and upgrade to materials that are currently approved for the application.

There are also a number of code restrictions concerning the transition between dissimilar types of Pipe, by example, the codes expressly prohibit the use of PVC Female threaded fittings.

The code also prohibits directly glueing dissimilar plastics together.

[zelmo]

Thank you very much. I think I spent 20 hours searching the internet to find what you described so well.

[kactuskid]

Thanks a lot Lazypup for all the great explanations, I learn something new here all the time.

[LazyPup]

While we are discussing the characteristics of pipe there are a couple other terms we should discusss.

"SCHEDULE" We primarily think of the word schedule in terms of a timetable, but in fact the word schedule also means "a list or catalog".

In the Plumbing Industry Pipe is defined by Nominal trade size and the ASTM Schedule defines the exact inside diameter, outside diameter, wall thickness, temperature rating and pressure rating for the pipe. In a nutshell, the higher the schedule number the thicker the pipe wall.

The schedule ratings common to the plumbing trade are Sched. 10, 20, 40 & 80 and in industrial or municipal applications we often see sched. 100, 120, 200 and rarely sched 300.

When a pipe is manufactured to meet a certain schedule it is exactly the same size whether the pipe is PVC, CPVC or ABS.

CTS The CPVC pipe we commonly find in the local hardware or home supply is technically not pipe, but rather it is tubing and is listed as CPVC-CTS (CTS=copper tube standard) While pipe is sized by its Inside diameter (ID) tubing is sized by its outside diameter (OD).

When buying copper we must check the labelling very carefully because seamless roll copper is available in both copper PIPE (ID dimension) and copper tubing (OD dimension).

When looking around your local home supply you will also see PVC SDR pipe. SDR Pipe is manufactured to the ASTM-SDR standard (Size dimension Ratio). The wall thickness of SDR pipe is determined by dividing the outside diameter of the pipe by the wall thickness. Thus a 4" SDR-30 sewer pipe will have a wall thichness equal to 4 / 30= 0.133"

In some jurisdictions SDR pipe is suitable for the house sewer or for construction leach beds for a septic tank.

ALL PVC pipe used in the DWV system within the confines of the structure must be PVC sched.40 ASTM 2665 DWV grade.

You may use both CPVC-CTS & CPVC sched.40 to construct the potable water distribution system.

[zelmo]

Sorry, LazyPup, I must be dense. I still don't see the logic in not allowing pressure pipe to be used in DWV. I know the difference in the fittings, but just don't see why you can't use the better stuff in a less demanding application. (Other than the code says you can't.)

[HayZee518]

Doesn't DWV mean domestic water & vacuum?

[LazyPup]

Lets begin by answering Hayzee's question first.

The designation DWV is Drain, Waste & Vent.

Many people are under the false assumption that PVC pressure pipe is a better grade of pipe than PVC-DWV pipe, but in truth, such is not the case. In fact they are both the same pipe so now the obvious question is, why would the standards define Pressure pipe versus DWV pipe? In a nutshell it has to do with the sizing.

PVC pipe is made to the sizing specifications set forth in the ANSI IPS (Iron Pipe Standard) listed by "schedule" or tables of standard dimensions & specifications.

The ANSI Schedule table lists the dimensions for all IPS pipe sizes.
1/8", 1/4", 3/8", 1/2", 3/4", 1", 1-1/4", 1-1/2", 2", 2-1/2", 3", 3-1/2", 4", 5", 6", 8", 10", 12", 14", 16", 18, 20" & 24"

The schedule table then lists each size and the dimension specificatins. Here is an example of the dimension specs listed on the Schedule 40 tables for 1/2"

1/2" Nominal Schedule 40-
O.D. 0.840 AVG.I.D. 0.602 Min. Wall Thickness 0.109 Nominal Wall Thickness 0.170

The sizing standard holds true whether it is PVC pressure pipe, PVC-DWV pipe, ABS pipe or CPVC pipe.

Pressure pipe is manufactured to Schedules 10, 20, 40, 80, 100, 120, 200, and 300. (Normally sched.10 & 20 pipe is only used as electrical conduit).

The ASME (American Society of Mechanical Engineers) and the ASSE (Amercan Society of Sanitary Engineers) limits DWV pipe to Schedule 40 only.

It further limits DWV pipe to sizes:
1-1/4", 1-1/2", 2", 3", 4", 6", 8", 12" 18" & 24".

Understanding that sanitary fittings will only be manufactured to fit the approved DWV pipe sizes, the Plumbing codes then insist that all pipe and fittings used in the DWV system MUST BE listed as DWV pipe & fittings. This is to insure that we would not mistakenly use pressure fittings in the DWV piping system.

To further define the distinction between pressure fittings and DWV fittings all pressure fittings are listed by the angle of the bend, I.E. a 90deg elbow, a 45deg elbow, etc.

DWV fittings are listed by the fraction of a circle that the angle represents, thus a 90deg sanitary fitting would be properly indexed as a 1/4bend. (360deg / 90deg =4 or 1/4 of a circle)