Minimum continuous flow rate

[Richarlison]

Hi all,

I was asked to size an OH1 centrifugal pump for a particular service. In the pump datasheet, why does the client states that the Minimum Continuous Flow (MCF) of the pump needs to be added into the rated flow rate (e.g. Capacity in m3/hr = 60 + MCF). Any rationale for this, and what will happen if I did not add the MCF of the pump to the required flow rate? And for the second question, does a submersible vortex pump have a MCF, and does it need to be added into the flow rate during pump selection? How about a VS4 pump?

Thanks all!

 

[shvet]

does a submersible vortex pump have a MCF

Yes, it does. MCSF is related to internal water recirculation inside of impeller.

chap. 5

https://a.co/d/ctl4HuO

 

[georgeverghese]

Its probably because the client intends to install a simple orifice plate on the min flow recycle line. This way of enabling min flow is somewhat wasteful on power as it continues to recycle at some flow not dissimilar to MCF at design case flow.

 

[LittleInch]

I agree with George.

You should ask them if they've considered an ARV (automatic recirculation valve). Payback could be very quick and I don't think we should be wasting energy in this way.

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

 

[MJCronin]

Agree with LittleInch ... ARC valves are an important option when considering min flow configurations

The reason that the ARC valves exist is because compared to an orifice, the payback period is very short

Ask an ARC valve vendor to help you prepare a calculation to show payback period for your particular situation

Also, consider the additional cost of a VFD (with a small RV) as compared to an ARC valve configuration ... this might be cheapest of all, if you pump is configured to operate away from its BEP ...

MJCronin
Sr. Process Engineer

 

[shvet]

ARC and similar self-controlled devices are applicable for clean fluids only. While it is supposed to be a sump pump. Even orifice might not be a proper choice depending on final shape&ID.

Every device has its application area. Do not confuse OP.

https://www.eng-tips.com/viewthread.cfm?qid=501898

 

[Artisi]

Ask whoever put the data sheet together what they mean. In many cases the "experts" putting the spec. together haven't a clue about they are specifying or why.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[Heaviside1925]

OP,
To answer your original question, the client is communicating the need for 60m3/hr downstream of the pump but the pump will have a MCF. Since MCF is recirculated, it is not available downstream for whatever the client needs it for. These two values need to be added together so the pump is rated to flow required + MCF. The other commentors have recommended a ARC and even though these are great for some services, others not. ARCs are mechanical devices and they do fail, additionally if your client's maintenance folks are not used to adjusting and working on one it can do more harm than good. (I have seen multiple ARCs bypassed in the field for this exact reason) Another option mentioned was an orifice, these too can be an issue in dirty service because the can become clogged. The least efficient but most bulletproof method is a slip stream, I've seen them valved and non-valved. Operators and maintenance seem much more comfortable with this arrangement especially if a roto meter can be installed and they can set and verify the MCF rate.