DWV Pipe Under Pressure? 1

[esass13]

I have a 2 filters that were installed using 1.5" DWV pipe. I can't seem to find any specs or pressure ratings on DWV pipe. Although the pipe does have 1.5" SCH 40 PVC........DWV. In another place the pipe is labeled PSI 330 @ 73 degrees. Why would DWV pipe be rated for 330 psi? This is really throwing me. It seems the pipe is ok for pressure situations (as it's already installed), but I'd like to make sure it's alright over the long run.

Any thoughts?

Thanks

 

[rconner]

It would appear at least some of your piping is claimed (by the markings on same) to be (water) pressure-rated. While not purporting to be an expert, I think you are asking a good question as while some used in such applications might be pressure rated I do not think all DWV (Drainage Waste Vent) pipes are necessarily pressure rated. I believe pressure rated pvc pipes by most pressure pipe standards require a formulation (amount of fillers and specific resin etc.) that have to be at least sort of proven with at least some various sustained and other pressure testing. I suspect at least in the past DWV pipes could in some cases e.g. be formulated with more amount of fillers and/or other resins that may be more economical to produce (yet not necessarily helpful for long-term pressure performance). If you can find e.g. a specification number such as ASTM... etc. also marked on the various pipes, reference to that specification/scope etc. will likely provide more information about the specific pipe involved.

 

[bimr]

Since you have provided incomplete details on your pipe, it is not possible to provide the design rating.

The 330 psi is probably not really the pipe pressure rating. The 330 psi is probably the quick burst pressure rating.

This was discussed in another thread:
thread164-155889

http://www.eng-tips.com/viewthread.cfm?qid=155889&page=1

Pressure class or pressure rating of the PVC product refers to anticipated steady-state continuous operating capability and are based on long term material strength. Desing for long term, steady state operating conditions based on short term strength of PVC pipe would be inappropriate. The Pressure class or pressure rating takes into account the long term response of PVC pipe to applied stress.

The quick-burst pressure or short-term strength divided by a safety factor of 2.5 will yield the corresponding short-term pressure rating of the pipe. The short-term pressure rating should be considered the design surge capacity limit for PVC in a transmission application. The short-term pressure rating represents a level approximately 25%a above the pressure rating for each rating class.

http://www.engineeringtoolbox.com/pvc-cpvc-pipes-pressures-d_796.html

 

[esass13]

thanks for the help!

complete pipe details as shown on pipe:
1 1/2" SCH 40 PSI 330 @ 73 PVC 1120 ASTM D 1785 (CO. LOGO) ASTM D 2665 (CO. LOGO)S.P.C. (can't make out the rest)

I can't make out the manufacturer or I'd just call them. Could it be that the pipe is dual purpose?

 

[rconner]

I think it is possible at least for a pipe marked with both standards (at one time I think ASTM D2665 even contained the phrase, ""It is common practice to dual mark Schedule 40 DWV and potable water piping in which compliance with each applicable standard is met.")

 

[jdarco]

Your pipe is pressure rated to a maximum 330 psi at 73 Deg F. Pressure rating gets derated for higher temps. Also, the type of fittings you have installed make a difference as well. If they are schedule 40 fittings, you have a pressure rated system to the limits of the lowest rated component (likely a valve or union). If they are DWV pattern fittings, thats another story. While they will hold some pressure (think of a 10 story building head pressure), they are not designed or warranted for pressure.

It is common for plumbers to use PVC 40 pipe for DWV applications. Many manufacturer's make "dual mark" pipe for both pressure and DWV applications. They also make "foam core" which has internal fillers and foam, hence reducing the amount of virgin resin required (and the cost) and only rated for DWV applications. Home Depot typically has this pipe in stock. But it is clearly labeled as such.

Check your fittings, they are really the determining factor

 

[bimr]

Here is a reference that may help you:

http://www.us.piping.georgefischer.com/external/us_handbook/03.pdf

The pressure ratings of thermoplastic pipe represent the maximum allowable operating pressure within a piping system for water at 72°F (23.4°C) based upon a service factor of 0.5.

Plastic piping systems must be derated for surge pressures in addition to a temperature derating. It is best to consider the actual surge conditions that the piping will be exposed to. In addition, substantial reductions in working pressure are advisable when handling aggressive chemical solutions.

One would suspect that the water treatment supplier is using a high velocity (higher than 5 ft/sec) in the filter piping to save cost. That high velocity combined with the cycling of valves will lead to a substantial derating of the pipe pressure rating.