Set point of the minimum flow by-pass valve 1

[roteng518]

We have pump datasheet from the vendor that shows the minimum flow (MCSF)is 21m3/hr, while on the pump vendor IOM manual the set point of the minimum flow for the by-pass valve controller is 34m3/hr, which is 40% of the pump rated flow.

My question is: how to determine the set-point for this type of by-pass valve? Shall we use the MCSF on the data sheet or shall we request pump vendor to determine?

 

[micalbrch]

The only one who can answer your question is the pump vendor. The data sheet was most probably filled for a specific job while the manual is more general. They might use a different bypass valve or at least a different setting. Ask them.

 

[SREisme]

Preferably you would have a company standard of your own for minimum flow based on suction specific speed, specific speed, and BEP. Barring that I would ask the vendor what the minimum flow for long term reliable operation is, not short term failure, and set the flow rate at that. 40% of BEP is lower than anything we would use for our pumps as a general rule.

 

[BigInch]

20 m3/h would typically be a minimum stable flowrate for your pump, but the bypass flow should only be operated that low when starting or stopping the pump, perhaps for a maximum time of 10 minutes or so. 40% could be used for temporary low flow conditions that would very soon return to more normal operating ranges of 60% BEP or above. Any need for continued operation between 60 to 80% of BEP should be subject to review by anyone interested in controlling excessive maintenance and power expense. Operation for extended times should be above 80% BEP to minimize maintenance expense and stay within optimum efficiency thereby keeping power costs within acceptable levels.

**********************
"The problem isn't finding the solution, its trying to get to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[pumpking]

Been touched on in an early reply, you need to speak to the manufacturer, for a small centrifugal (up to 6" single stage at set 2900/3600 rpm speeds, rule of thumb for minimum flow is 10% of flow at best efficiency point for selected Impeller, however, there are a number of factors to consider, so manufacturer can help. Later posts are also correct, running at these points are also detrimental to the long term life of the pump, so specific considerations have to be taken into account.

Ash Fenn

http://www.cdrpumps.co.uk

 

[rshayesteh]

As pumpking also mentioned, the minimum flow normally ranges from 10% for small pumps to 35% for the large ones. If 34 m3/hr is 40% of rated flow, 21m3/hr would be around 24% which looks more common for the minimum flow. anyhow ask the manufacturer for clarification (and plz reflect the answer here)


Reza