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

 

[LittleInch]

My way of thinking is that in the direction of flow you have the isolation valve and then the check valve.

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.

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

 

[pennpiper]

For check valves at Pump Discharge it should be: Pump, then Check Valve, then Isolation valve
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

 

[bimr]

Both a check and gate valve should be installed in the discharge piping with the check valve placed between the pump and the stop valve to protect the pump from reverse flow and excessive back pressure.

http://www.flowcontrolnetwork.com/pump-guy-mailbag-considering-check-valve-location/

 

[LittleInch]

The tank I'll give you, but in reality how many times is an NRV ever removed from pump??

So in two posts you have two different ways of doing it - never simple eh.

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

 

[europipe]

I think you're alone now, little.
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.

 

[LittleInch]

"in many cases a pressure relief drain is placed between check- and isolation valve"

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.

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

 

[donf]

I agree with Pennpiper (pump-check valve-isolation valve). In a parallel pump arrangement, having an isolation valve between the check valve and THE OTHER pump allows the defective check to be replaced, while the OTHER pump is pumping.

donf

 

[LittleInch]

You guys have a lot of defective check valves.....

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

 

[europipe]

Check valves are never 100 percent reliable.

 

[alienitmeca]

Thank you everyone for your responses,

it's been quite an interesting discussion, very informative as well

 

[BigInch]

LittleInch, you give up too easily.

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.

 

[LittleInch]

BI welcome back, haven't seen you on here for a while....

Fully agree, makes sense to me.

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

 

[BigInch]

Thanks.
I've had some other priorities to attend to lately.

 

[Krausen]

It really does depend on the system layout. The pump + block valve + check (or meter + block valve + check) sequence is the best choice IMO for reasons LI explained, but should only be used in systems where the piping/equipment can be blocked in elsewhere without suffering a major downtime. In my work we apply this layout about 80%-90% of the time. We've had clients who are adamant on flipping the block & check, without appealing to reason other than "we've always done it that way".

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.

 

[BigInch]

Then you have the same problem when your block valve needs to be repaired.

 

[georgeverghese]

In many cases, a check valve has a process safety function, and this may in some cases where the consequence of a check valve failure poses some safety and loss of production risks, demand some means of isolation on BOTH sides of the check valve to run a leak integrity test and have it removed for repair where necessary. Else you have a large volume of gas or liquid to dispose off before this test and removal can be done.

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.

 

[flukeynub]

This is the exact question I've been asking some of my firm's senior engineers to shed some light on in the last two weeks without much luck.

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!

 

[lilliput1]

Pump, check valve then isolation valve so check valve can be serviced without draining the line. The isolation valve is normally left open all the time. It is closed only when pump or check valve servicing is required. The check valve insures no back flow when pump is stopped and there is a parallel pump operating. Typically for chilled water service, the chiller automatically starts its associated pump and the pump isolation valve is open.

 

[bimr]

Check valves are not considered to be reliable so process safety engineers do not use check valves for process safety functions.