Irregular Pump Flow
Irregular Pump Flow
(OP)
Can anyone explain the following behaviour?
Grundfos borehole pump with a flow of approx 2 m3/hr. Discharges to a tank open to atmosphere approx 300m away. The pump is fixed speed and the whole system operates manually. After between 15 and 90 minutes of pumping, the flow suddenly reduces to nearly zero for approx 1s, followed by a surge for approx 1s or 2s. Behaviour repeats at irregular intervals but with increasing frequency and severity. After operating in this manner for approx. half an hour the flow stops completely for approx 4s, followed by a surge. The pump was stopped at this point. Behaviour repeated over several tests with not enough data to discern a connection between pump rate and how quickly the problem presents.
Some possibilities:
Excessive drawdown in the borehole leading to cavitation or air entrainment
Irregular supply voltage
Trapped air in the pumping main
Any thoughts on the above would be appreciated, as would suggestions for anything else it could be.
Thanks
Grundfos borehole pump with a flow of approx 2 m3/hr. Discharges to a tank open to atmosphere approx 300m away. The pump is fixed speed and the whole system operates manually. After between 15 and 90 minutes of pumping, the flow suddenly reduces to nearly zero for approx 1s, followed by a surge for approx 1s or 2s. Behaviour repeats at irregular intervals but with increasing frequency and severity. After operating in this manner for approx. half an hour the flow stops completely for approx 4s, followed by a surge. The pump was stopped at this point. Behaviour repeated over several tests with not enough data to discern a connection between pump rate and how quickly the problem presents.
Some possibilities:
Excessive drawdown in the borehole leading to cavitation or air entrainment
Irregular supply voltage
Trapped air in the pumping main
Any thoughts on the above would be appreciated, as would suggestions for anything else it could be.
Thanks





RE: Irregular Pump Flow
Plan B - run it at 1m3/hr by throttling a discharge valve somewhere along the way and see how long it lasts then.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Irregular Pump Flow
Independent events are seldomly independent.
RE: Irregular Pump 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.)
RE: Irregular Pump Flow
RE: Irregular Pump 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.)
RE: Irregular Pump Flow
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Irregular Pump Flow
LittleInch- thanks for the advice. Replacing the valve is certainly necessary. I found out today that the pump has apparently been fine since the last test, so maybe I'll just put it down as an anomaly.