Check valve Position
Check valve Position
(OP)
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
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





RE: Check valve Position
The reasoning is that the check valve is difficult to drain past and if you shut the isolation valve you can lock in fluid between the two. Hence if you drain the pump, not all the fluid leaks or can suddenly escape.
Do it the other way around and the fluid is able to flow from the isolation valve to NRV side to somewhere downstream.
Inlet to a tank would be the same thing in direction of flow - isolation then NRV then tank.
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RE: Check valve Position
Check valves tend to fail more often the isolation valve. So if you have to remove the NRV at a tank you will risk draining all of the fluid in the Tank if you place the isolation valve as Little said.
Rule to remember is the isolation valve should always protect the greater inventory of product
Sometimes its possible to do all the right things and still get bad results
RE: Check valve Position
http://www.flowcontrolnetwork.com/pump-guy-mailbag...
RE: Check valve Position
So in two posts you have two different ways of doing it - never simple eh.
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RE: Check valve Position
I always saw it like mr. Pennock sais.
Also, for discharge at a pump, in many cases a pressure relief drain is placed between check- and isolation valve.
RE: Check valve Position
That's my point - if you don't put your pressure relief and drain between the two you can run into problems. Put it the other side and you don't need to bother if the single PRV and drain connection is on the other side.
From a purely process view, either location is fine - a lot depends on particular piping layouts and orientations.
I've seen both and ultimately this is a view the designer needs to take, but there are no "rules" to this, only custom and practice.
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RE: Check valve Position
donf
RE: Check valve Position
Remember - More details = better answers
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RE: Check valve Position
RE: Check valve Position
it's been quite an interesting discussion, very informative as well
RE: Check valve Position
The preferred arrangement should not be decided based on facilitating check valve, or any other valve's maintenance. It is far more important to facilitate pump maintenance, as the pump will statistically be the most frequent item requiring break out maintenance of one sort or another. Pump, isolation valve and check is thus the preferred solution, as no pressure will be trapped between isolation and check valves nor will any pressure be in the maintenance's crews face when breaking out the pump. If you do it the wrong way, then you must add the extra vent valve to release the resulting trapped pressure.
If there is any concern about draining adjacent piping or tanks, provide an appropriate spectacle blind.
RE: Check valve Position
Fully agree, makes sense to me.
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RE: Check valve Position
I've had some other priorities to attend to lately.
RE: Check valve Position
If you are flowing into a system that is not easily isolatable (e.g. injection into a mainline that runs 24/7), the pump + check + block valve is the better option due to having to shut down an entire mainline in order to service a defective check valve.
RE: Check valve Position
RE: Check valve Position
The periodic scheduled verification of a check valve's integrity in such services has increased in importance in the last 10-15years or so. On the other hand, manual isolation valves are not process safeguarding devices.
RE: Check valve Position
I debated this question with myself at my last job (was an operations engineer) and decided at the time I preferred pump/check/iso mainly because we saw many more problems with check valve failures than pumps/iso valves. I had to redesign an acid scrubber spray system to allow for check valve replacement as process system up time was significantly more important than ease of pump maintenance. Not to mention, for some reason, none of the pump/check/iso configurations at that site had a vent which is why I even thought about this in the first place.
Thanks for the opposite thought process perspective!
RE: Check valve Position
RE: Check valve Position
RE: Check valve Position
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
RE: Check valve Position
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
RE: Check valve Position
If there is a requirement to eliminated the pressure trapped between isolation and a check valve, a small drain line w/valve is included.
RE: Check valve Position
RE: Check valve Position
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
RE: Check valve Position
So exchange a checkvalve is easier to do, like mr. Pellin sais.
RE: Check valve Position
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
RE: Check valve Position
How do you relieve pressure when you line break the pipeline for maintenance?
Link
RE: Check valve Position
RE: Check valve Position
https://www.google.com/?gws_rd=ssl#q=Line+Breaking...
RE: Check valve Position
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.
RE: Check valve Position
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.
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Also: If you get a response it's polite to respond to it.
RE: Check valve Position
RE: Check valve Position
RE: Check valve Position
RE: Check valve Position
RE: Check valve Position
RE: Check valve Position
RE: Check valve Position
At least in Shell, wafer style checks were removed from their piping classes since the year 2000 or so.
OpCos = Operating Companies.
RE: Check valve Position
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&rct=j&q=...
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Check valve Position
They have also longer bolt lenghts.
RE: Check valve Position
Mostly they refer to flangeless valves, but clearly the longer the bolt the worse it gets in terms of expansion in the event of fire.
My guess would be if you more than double the length of the bolt then you start to run into that issue, but haven't done any calcs on that.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.