Boiler feed pump keeps failing

RayWohlfarth

I have run into a puzzling problem and hope someone can help me figure it out. We have a commercial steam system and the boiler feed pumps are binding after only a few months. The system pressure is 2 psi and there appears to be no flash steam. We cleaned and flushed the boiler feed tank and I am befuddled. Any ideas?

retiredguy

Have you checked the amperage of the pumps motor? If it is too high it could be an indication of cavitation which will ruin the pump. Also, if the pump is noisy, it could also be from cavitation. Anytime I installed a condensate pump I installed a discharge valve similar to a square head gas cock so I could limit the pumping capacity and reduce the pumps ability to cavitate.

Jamie Hall

I'm thinking cavitation too. Take a look at the inlet ends of the impellor vanes. There should be no sign of erosion or pitting -- even a little means that they are cavitating. The thing about cavitation is that it doesn't just damage the impellor. It can also put remarkably high lateral -- thrust -- loads on the bearings, which can damage them.

Presumably the feed tank is at atmospheric pressure and the condensate is hot? There should be several feet of head -- at least -- at the pump inlet.

clammy

Being you have a boiler feed pump I would gather that you have f and t traps also . Are the f and t piped w a drip and a strainer and does the boiler feed pump have a basket strainer or wye strainer to catch the debrie that enters . A plug cock and gauge to ensure the pump has some restriction on it . Has the amp draw and voltage been check and are in line w motor ratings ? I see the boiler feed pump sized correctly a undersized feed pump receiver will short cycle the pump while not having enough volume that the boiler needs which will make the pump run more often and pump less volume then is needed . If this was a on going constant issue that’s where I de be looking and possibly not blaming the feed pump . Has the reservoir been flushed and hosed out w all the mud and nastiness removed in some cases this has to be done monthly espically if it’s a small boiler feed pump and does not have a seperate deaeration receiver. Are they using a lot of chemicals in the make up water and what’s the condition of the mains and wet return ,no insulation increase rust and sediment in mains and return which in turn bring more crude back to your boiler feed system . Food for thought
Peace and good luck clammy

RayWohlfarth

@retiredguy and @Jamie Hall thanks we checked it and everything was good 

JUGHNE

I have a single feed pump feeding 2 small boilers.

Each has a solenoid valve.

The flow has to be throttled back a lot or it will kill the steam.

I added a pump by-pass that feeds back into the tank.

This allows the pump to run a full flow of water when operating.

IDK if this would help your situation or not.

Is the small water tube (primer??) on the bottom of the pump passing water?

RayWohlfarth

pedmec

What do you mean when you say binding. Just want to clarify the actual issue. Not throttling back can over amp and burn out the motor which i wouldn't call binding binding but you might. Cavitation which could mean not enough return condensate entering the eye of the impellar, below its vapor pressure, and would be seen by the pitting associated with it.

Are you replacing the pump assembly when you change do the repair?

Pumpguy

The open impeller design of this pump is one I'm not familiar with. That said, I am very familiar with cavitation damage and see no signs of it here.

I too would like a better description of your term 'BINDING". Does this mean mechanically locking up or seizing, or something else?

I am familiar with the term AIR BINDING where the pump will spin but not pump due to the presence of air in the case; not enough water.

RayWohlfarth

@pedmec and @Pumpguy We have the balancing valve partially closed the amperage is correct. Its like the impeller is making noise, almost like its not free. The maintenance person flushed the tank refilled it. . I was wondering if the pump ran without water if that is what is causing it. I did notice the water level in the tank was very low

EBEBRATT-Ed

@RayWohlfarth

You could install a low water cutoff on the tank to shut the pumps down if the water level gets low. I would check with the pump manufacturer to see what the minimum height (head) needs to be on the suction side of the pump (this will change with the condensate temperature) I would also check the boiler feed tank vent for steam. You may have some trap(s) blowing through which will overheat the condensate.

pedmec

you should have a automatic fill on the tank to prevent the low water condition. most have float type but you can have a water level control to open a solenoid on demand for make up water.

If you have a low water condition in the tank you need to address it. it should always maintain a minimum water level in the boiler feed tank. the seals could be failing due to low water the tank and causing the steam to flash. i would check to make sure the water supply to the tank and the water level controls are feeding water to the tank. Then i might consider looking for a leak if your constantly needing water. you could possibly be losing water depending how fast the level in the tank needs to be replenished. and underground leak on a return maybe. it be normal amount of loss depending on your system but i'm not there.

JUGHNE

Does the tank have provisions for a sight glass?

Pumpguy

Typically a pump run without water will cause the shaft seal to overheat and start leaking.

IMO, if you don't have a leaking shaft seal, your pump has at least enough water to keep the seal wet.

RayWohlfarth

So I went to job site and found dirt was inside the pump volute Once we cleaned it it worked fine The guy went said he flushed the boiler feed tank last Obviously not Thanks for the help