Reasons why the condensate- or boiler-feed pump is misbehaving, and where to look for solutions

HeatingHelp

Reasons why the condensate- or boiler-feed pump is misbehaving, and where to look for solutions

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Bugz

Is my condensate pump louder because of the weather?

Youssef1971

Our feed pumps continuously cavitated , can we know the reasons ?

Jamie Hall

The overall reason is low "net positive suction head". Which, I realise, isn't a bit helpful unless you know what it means.

Which is that there must be a minimum absolute pressure at the inlet to the pump, which is dependent on the pump construction and -- assuming water -- the water temperature. That's absolute pressure, not gauge pressure.

Why might this be the case? One reason is excessive restriction in the inlet piping. One reason is too much suction lift. A very common reason in heating applications is inadequate static head (the level in the tank vs. the elevation of the pump) combined with warm or hot water.

There are secondary problems, too -- such as an elbow too close (less than 10 pipe diameters) from the intake, or a valve which isn't full port within the same distance.

Good general practice would be to ensure that the pipe is straight and unobstructed for at least 10 diameters before the pump and there is at least two feet of water over the inlet at all times, even for cold water -- and more for hot water.

dopey27177

If your condensate temperatures are above 160 degrees and if the pump is a rotating at 3200 rpm and above steam is forming in the eye of the impeller therefore the pump can not pump water.

The steam caused the prime in the pump to be lost.

I assume you have a steam system with steam traps, if so look for defective steam traps that are passing steam, If this is a system that supplies heat for a building only, lower the steam pressure to no more than 2 PSIG.

Jake