Protecting Variable speed pumps with low flow by-pass line

[Sahkah]

Hello experts,
Couple of constant speed pumps ,used in a heating system, are being replaced with new VFD pumps and so are the accompanied three-way valves converted into 2 way valves; my question is, is the existing low flow by-pass line need to be kept to protect the new pumps from critical low flow ? please advise ..Thank you

 

[Artisi]

Without full details, I would say - yes the pumps need to be protected from critical low flow.

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.)

 

[TugboatEng]

If the power input in to the pump at low speed is able to be dissipated to the ambient environment while staying at a temperature below the pump or fluid's max allowed, then you can operate without bypass.

 

[1503-44]

The low flow limit for a vfd controlled pump is very much lower than a constant speed pump. The low flow limit of a vfd pump will probably not be sufficient to try to keep your process alive. With that in mind, it's probably better to simply turn it off. If for some reason you need to maintain process circulation, it will most likely be a flow rate much higher than the low flow limit of the pump, so you will probably be shut down due to process considerations before ever reaching vfd low flow limits.

 

[Sahkah]

Thank you all for your inputs .