Check valve Position 8

[alienitmeca]

Hello,

When designing your piping layout, one would certainly have to use a fair amount of valves of various types (check valves, gate valves, butterfly valves...) to choose one type over the other demand some thinkig along with good engineering skills and operating conditions, My question is included in this department:

when on uses a check valve along with a gate valve (at the outlet of a pump, inlet of storage tank...) how to know when to put check valve then put gate after in it or is it the other way around ? Could you help me how to decide in this matter.

Thnk you

 

[JJPellin]

I work in a large US oil refinery. We have about 1600 centrifugal pumps. All of them, except for two have the check valve between the pump discharge flange and the block valve. This is a requirement of our standards. Perhaps some references could help.

API Recommended Practice 686; Second Edition

“A check valve shall be installed in the discharge line of all pumps, compressors or blowers, whether centrifugal or rotary, unless there is no possibility of a reverse flow or pressure surge (such as water hammer) under any conditions. The check valve shall be located between the machine discharge flange and the discharge block valve.”

Hydraulic Institute Standards for Centrifugal, Rotary & Reciprocating Pumps, fourteenth edition

“A check valve and a stop valve should be installed in the discharge line. The check valve, placed between the pump and the stop valve, is to protect the pump from reverse flow and excessive back pressure.”

Piping Design for Process Plants; Rase and Holmes; 1963

“Place check valve between discharge nozzle and gate valve to prevent liquid backup when pump stops running.”

I have worked with many thousands of centrifugal pumps over the past 27 years. I don’t recall ever seeing the check valve installed outside of the first block valve.


Johnny Pellin

 

[JJPellin]

I pulled another couple of books off my shelf.

Centrifugal Pumps; Karassik and Carter, 1960

“Generally, both a check valve and a gate valve are installed in the discharge line. The check valve is placed between the pump and the gate valve and protects the pump against reverse flow in the event of unexpected driver failure.”

Pump User’s Handbook; Bloch and Budris, 2004

“Gate valve should not be between check valve and pump.”

Does anyone have a published reference or standard that shows the check valve outside of the block valve?


Johnny Pellin

 

[bimr]

Agree with JJPellin. Have never witnessed any other installation.

If there is a requirement to eliminated the pressure trapped between isolation and a check valve, a small drain line w/valve is included.

 

[lilliput1]

Pressure between check valve and closed block valve would only be a concern is the trapped fluid is colder than ambient and it expands as it heats up.

 

[BigInch]

All those references ... and there is no accompanying logic to justify the requirements???

The hydraulic facts are that a check valve installed downstream of the pump and block valve is equally adept at stopping backflow to the pump as a check valve upstream of the block valve ... unless the block valve is already closed, but that would mean no backflow is possible at all

 

[europipe]

BI, I think like most of us a checkvalve is no reliable option to close a system, a blockvalve is.
So exchange a checkvalve is easier to do, like mr. Pellin sais.

 

[JJPellin]

We fail check valves quite often. Some of our check valves are designated as critical checks for mitigation of process risk associated with back-flow. Those valves often have to be pulled and inspected on some defined frequency.

Most of the time, the process downstream of the block valve can only be taken out of service at a major turnaround (every 4 to 6 years). I have never heard of any problem with stored pressure between the check valve and the block valve. If the check valve is outside of the block valve and it fails, I have to shut down a process unit (potentially costing millions of $US). If the check valve is inside of the block valve, I might have to use a short spool with a bleed valve to eliminate the possibility of stored pressure trapped between the valves. This is not a problem for me. Putting the check outside of the block valve seems to have a huge potential downside (unit shutdown) with no real upside. The fact that every standard I can find goes to the trouble to specify this arrangement suggests that a lot of people have reached that same conclusion.

Johnny Pellin

 

[bimr]

Regarding: Pressure between check valve and closed block valve would only be a concern is the trapped fluid is colder than ambient and it expands as it heats up.

How do you relieve pressure when you line break the pipeline for maintenance?

Link

 

[lilliput1]

One could slowly unbolt the flanges so the fluid leaks out to relive the pressure. Or maybe the pump needs to be serviced because fluid has already leaked out and relived the pressure!

 

[bimr]

Last time I checked, it is 2016 and employees working for responsible corporations have line breaking/opening procedures for safety of the employees working on piping.

https://www.google.com/?gws_rd=ssl#q=Line+Breaking/Opening+Process&start=10

 

[lilliput1]

bimr,
You are right. Steam pipes and hot water pipes need to be able to relieve pressure so as not to cause injury when disconnecting piping or equipment. Provide drain valves and blow off valves at strainer. Locate between equipment and block valve.

 

[LittleInch]

I can certainly see the point here and maybe what it highlights is the difference between process plant type pumps and pipeline type units. Use of check valves for a process function is different to using it for a pressure break / safety function. You can take credit for a check valve to reduce back flow, but not to seal.

Having said that sometimes they do work very well and the key point is to look at your particular system and piping layout and make sure you can vent and drain between a check valve and its downstream block valve. If your particular use of check valves is such that they are seen as critical to the process, used in anger a lot and hence more likely to fail, then suitable isolation needs to be in place and for many this will be between the pump and the pump isolation valve. For others it might not or the check valve is there for an extreme event and not used in anger very often so would be expected to last for a long time and can be upstream or downstream.

So the key answer (for me) to the original question is look at your systems and understand the issues over space, potential for removal or servicing, isolation requirements and impact on the process and the ability to drain sections of piping when you install check valves.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

Whilst on this topic of check valves, though not the topic of discussion, some OpCos have stopped the use of wafer style check valves for at least 10years now when in flammables service.

 

[europipe]

George, can You explain why, and why 10 years?

 

[MickMc]

It is common for wafer style valves not to permitted in hydrocarbon service as in fire case the stud bolts are unprotected and liable to fail first.

 

[europipe]

Ah, the fire situation, what is OpCos?

 

[BigInch]

Perhaps it means operating companies.

 

[europipe]

That's a wide understanding

 

[georgeverghese]

Yes, long bolts on wafer style checks tend to loosen more during a fire...

At least in Shell, wafer style checks were removed from their piping classes since the year 2000 or so.

OpCos = Operating Companies.

 

[LittleInch]

I've seen pictures and videos of long bolt wafer checks and wafer valves during a fire compared to other bolts and it's alarming. Unless there is no possibility of a pool fire underneath it or you fire protect it, this would / should come up in a HAZOP or similar safety review of the plant design or just be banned for new installations.

See this - slide 10 is the key one comparing a "normal" flange and a long bolt one.

http://slideplayer.com/slide/4731877/

This is a one page version of the same thing

https://www.google.co.uk/url?sa=i&r...ja9N3wuYbOAhWENJoKHWxeCGYQ5TUICQ&url=https://

http://www.aiche.org/sites/default/...vG1sJb0YDim81GWg&ust=1469255623469555&cad=rjt

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.