How to get constant flow

[RJSH]

Variable water level in a tank over the time. Need to get a constant Discharge Q by use of a submersible pump (150 gpm). The flow discharge to atmosphere pressure. What flow/pressure control valve should I use? Any suggestions on piping configuration?

 

[bimr]

One of the Cla-Val will do this:

http://www.cla-val.com/flow-control-valves-c-1_114-l-en.html

Another option if you want increased accuracy, is to use a control valve with a separate controller (with a 4-20ma output signal to the valve). The controller will allow you to set the flow rate. This option allows more flexibility.

 

[chicopee]

First do you need to have 150 gpm exactly at all water level conditions? Secondly, how critical to the process is the system that you require because looking at bimr's link to Cla-Val, that control valve seems very expensive. Also about providing more info about process type, tank size, max/min water levels, discharge hose type/size/length.

 

[RJSH]

The flow has to be close to 150 gpm. Forgot to mention the application is wastewater (belt filter press wash water drain). Pipe type is ductile.

 

[bimr]

You do not want any operating valve on this application because the solids will foul the valve.

I assume that you are pumping out of a sump where the drains from the BFP collect.

Select a pump that will provide you the 150 gpm at the pump operating conditions (static head and dynamic friction). Use a conductive level probe to measure water depth in the sump. If you are concerned that the flow will be too much, install a manual plug valve. You can throtttle the plug valve to reduce the flow if it too large.

Your sump should not be so deep that a few feet of water depth is going to make that much difference. You can also utilize a pump with a flat curve.

 

[LittleInch]

How much does the level change compared to your required discharge head?? If it is less than 10% (e.g level varies by 3m, differential head of pump is 30m) I wouldn't think this has much impact on your flow compared to other variables like temperature and water composition.

If you need a very close limit, then some sort of PD pump (diaphragm maybe) will give you a pretty constant flow regardless of inlet conditions.

Those pinch valves shown by bimr are good for slurries and waste systems - the more traditional control valve types are very likely to clog and wear. However many companies offer waste water valves - this is just one of many -

http://www.rossvalve.com/pdfs/RossWastewaterValvesBrochure2.pdf

Figure out you max and min head difference you need to control on - for lowest inlet level just write Min in the differential head box on your data sheet to be submitted to the vendors. Be aware it won't be zero so you may need to oversize your pump a little to cater for the worst case for the pump (minimum inlet level).

Piping - avoid lots of bends or tees and dead legs or vertical sections where stagnant flow can accumulate.


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