Drilled check valves for warm up

[Wkcoo]

Hi, i would like to propose drilling a hole in the check valves to warm up my pumps. I want to perform some calculations on hole size and whether my pumps will reverse overspeed, but not sure what references there are. Any input is appreciated

 

[LittleInch]

I've never quite understood this drilling holes in check valves as it seems to me to defeat the whole object of a check valve. A bit like not being able to shut an isolation valve fully.

but either way, when I've looked at this before you can find very little officially. Vendors are most reluctant to give any sort of reverse flowrate or RPM and how much resistance you get from the motor also seems to be highly ambiguous. Seals often don't like going backwards or couplings and you would probably invalidate any warranty.

If you need a figure I would go for max 10% of the forward flow or less, but this is just something to give you a guide. I guess one aspect that pumps are not designed for is sudden reversal when the pump starts and hence the hole in the check valve thing is difficult to control.

If you want to warm up the pump then you should do it properly and install a small pumped flow which feeds from inlet to discharge and can be interlocked with the main pump. IMHO.

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

 

[bimr]

What do you mean by "warm up my pumps".

 

[electricpete]

The typical scenario where this hole in check valve is useful is when several pumps are in parallel for pumping hot fluid with some of them running and at least one idle (standby).

In absence of a hole, the idle pump and its fluid can cool down towards ambient, which can create thermal shock to pump or system when you start that pump.



=====================================
(2B)+(2B)' ?

 

[1503-44]

I'm not following this at all. So this is to keep the pump hot, mostly pressured and turning a little backwards, backfeeding to its inlet when stopped?

Holes in check valves can be dangerous, as that is generally unexpected and usually triggers maintenance warnings.

 

[Wkcoo]

The scenario is same as what described by electricpete. The thought that I have now is to treat it as orifice sizing.

 

[TugboatEng]

Or a bypass line with a throttling valve. If you decide you're not happy with the flow from your hole buying a bunch of new disks can get expensive. If the hole is too large and you have some hypothetical 10 gpm more than you need at 100 psi differential x 5 offline pumps that's some 22.5 MWh of wasted power per year with 24/7 operation.

 

[JJPellin]

We commonly drill holes in our check valves to keep pumps warm. Use a standard orifice calculation to size the hole for 5 to 10 gpm. It will not roll backwards. The valve flapper will not be damaged. We probably have 500 pumps operating this way for 50 years.

Johnny Pellin

 

[Wkcoo]

Hi JJPellin, is there any consideration where to drill the hole? Should the hole be at the centre of the flap or offset to one side?

 

[Aub_Engineer]

A word of caution is for top suction/top discharge or multistage pumps this warmup configuration may not be sufficient. You may need to route your warmup lines through the pump drains to properly heat the whole case and fluid inside. There is an example in API RP 686 to follow.

 

[JJPellin]

Good point, Aub. This is not the best option for some pump configurations. I would drill the hole in the center of the flapper.

Johnny Pellin

 

[casflo]

To drill a hole in the disc of a swing check valve is also a way of avoid that it be oscillating, beating the valve seat, when the flow through the valve is low.
For example, in some nuclear power plants, there are turbine driven pumps in standby and it is necessary to keep warm the steam feeding pipe, circulating a low flow rate that passes through the swing check valves.

 

[georgeverghese]

Both methods seem to be popular:
drill a hole through the check valve
or
install a 3/4inch gate valve in parallel with the check valve, set slightly open and remove the handle to prevent tampering.
Have yet to hear of any cases with reverse flow of the pump with this trickle warm up stream.
Also enable a low temp permissive on the pump casing to inhibit pump start if the pump is not warm.

 

[TugboatEng]

A gate valve?

 

[georgeverghese]

A small bore globe valve will do just as well as a gate in this service.

 

[bimr]

Online discussion of the issue:

Link