Can an adjustable check valve be used as a relief valve? 1

[oddmanout]

Can someone here please explain the difference(s)if any between an adjustable check valve (ACV) and a pressure safety relief valve (PSV)? Can one be substituted for the other? If not, then what would be some typical applications for an ACV that a PSV would not be suited for and vice versa?

 

[pleckner]

Is this for an ASME coded vessel/system?

 

[Ashereng]

The quick answer is NO. An adjustable check valve can not be used to replace a PSV.

In simple terms, a check valve is a directional controller - flow is in ---> this direction.

A PSV ensures that a certain pressure is reached - if it is, the PSV relieves the pressure to another "system" (such as the flare).

The two are desgined to do different things (regardless of ASME coded or not).

Also, where I work, a PSV is an instrument, where a check valve is considered part of the line. The former is under the jurisdiction of I&C, the latter, piping/mechanical.

If you have an instrument guy/gal at your place, you may wish to talk to them - they can give you more info, and also show you the two different things.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[Ashereng]

Oops.

A PSV ensures that a certain pressure is reached - if it is, the PSV relieves the pressure to another "system" (such as the flare).

should read

A PSV ensures that a certain pressure is [COLOR=red yellow]NOT[/color] reached - if it is, the PSV relieves the pressure to another "system" (such as the flare).


"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[iainuts]

These comments are for US use only.

I just quoted this paragraph in a previous post. This is from ASME B31.3, (year 2004):

(a) Pressure relieving devices required by para. 301.2.2(a) shall be in accordance with the BPV Code, Section VIII, Div. 1, UG-125(c), UG-126 through UG-128, and UG-132 through UG-136, excluding UG-135(e) and UG-136(c). The terms "design pressure" and "piping system" shall be substituted for "maximum allowable working pressure" and "vessel," respectively ...

What this says is that some kind of pressure relieving device is required, but it specifically excludes the need for an ASME rated valve by excluding paragraphs UG-135(e) and UG-136(c). I don't have the BPV code handy to verify that, but I'm 99.9% sure my memory hasn't failed me there because we use non-code rated RV's for piping. Note however that an ASME code RV is needed to protect pressure vessels in the US. Not sure what is needed in other areas of the world.

Also, some of these "adjustable cracking pressure check valves" are specifically intended for use on instrument lines or any small diameter pipe or tube system. For example, Nupro (one of the Swagelok companies) makes a CPA Series "adjustable check valve". Another company, Generant, makes the "ACV" series which is a knock off of the Nupro CPA series. Both companies market these as relief devices for small diameter lines, for pressure up to 600 psi. I'm sure there are other manufacturers out there as well. Here's Generant's web page (can't seem to find the Nupro one.)

http://www.generant.com/ckvlv.htm

Note however that Air Products and Chemicals, Inc. has found that some of these very small relief valves (check valves) fail to operate well at low pressure. They tend to stick shut, and has suggested they not be used below 100 psig. See public disclosure here:

http://www.airproducts.com/Responsi...ty/ProductSafetyInformation/safety_valves.htm

So to answer the question, adjustable check valves are actually allowed by ASME B31.3 piping code and there are companies that make such things. They are not however, allowed for any ASME rated pressure vessel.

 

[dcasto]

You most certainly can use a check valve as an overpressure protection device. I've replace at least 100 3/4" thermal relief valves with adjustable check valves on pipelines, headers, DBB valves, and loading racks. As a matter of fact, think about how you could protect a liquid meter from thermal pressure if the meter had 100% benzene in it? How would you even test a device in that service?

 

[iainuts]

Hi dcasto. I'd agree with you there. I've used these things before too.

What valves did you use for thermal relief (ie: manufacturer and model)?

 

[Ashereng]

I am learning something new today.

I have never seen an adjustable check valve used as pressure relieving device. Evidently, other users do.


iainuts,

For thermal relief, I ususally use a 1C1 pressure relieve valve. That is 1" x 1" C orifice. Usually, the make I use is Farris and AG Crosby.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[pleckner]

In order to answer the original post properly, we need more information. At this time, the answers given are only guesses. There is no indication that this is for a pipeline or a vessel or what. That's why I asked the question I did.

 

[dcasto]

swagelock or whitey i believe.

 

[oddmanout]

My thanks to you all for your responses. These ACVs are being installed on both the shell-side and tube-side inlet piping to a shell & tube heat exchanger. Oxygen gas is being passed through the tube-side and water through the shell-side. The purpose of the ACVs are to prevent over-pressurizing either the shell-side and tube-side.

 

[pleckner]

This now sounds to me that this is an ASME coded vessel. If it is then you must use an ASME certified PSV.

 

[dcasto]

The check valve is for thermal relief, not fire.