Grundfos MQ3-45 B Pump Cycling

[Noke]

Hello everyone,

I purchased a house that had a MQ3-45B pump installed in line with the main city water. Within the last few months I have noticed that pumps cycles on and off repeatedly, but it doesn't do it every time. I believe I have narrowed it down to the cycling occurring after small water draw offs. After doing a little bit of research and speaking to a few people it seems like the problem might be the take up pressure bladder being under inflated.

I turned off the main water supply and unplugged the pump then drained the lines. I then knocked off the back cover and unscrewed the bladder/pressure tank (Part Number: 96565367). Water continued to drain out of the pump as well.

I unscrewed a little cap from the top of the bladder/pressure tank to expose what looked like bike valve. I was told to inflate the pressure tank to roughly 25 psi. Unfortunately I can't get the tank to take any pressure. I have tried a bike pump and a small compressor (the type found in a battery pack you would keep in your car). When I use a pressure gauge to try and check the pressure from that valve, I get no reading at all.

The tank seemed to have water in it so I shook it to try and get out as much of it as possible and tried again. The tank still will not take pressure. When I hook the compressor up to it and set it for 25 psi it immediately cuts off.

Is there something that I am missing or doing wrong? Is this bladder/pressure tank bad?

Thanks!

 

[Valveman]

Yes the tank is bad. But that may not be the only problem. Usually the electronics in those MQ pumps fail, which causes the pump to cycle on and off a lot, which will wear out a tank diaphragm. Your real fix and something that will last 30-40 years looks like this.

 

[Sponsor]

 

[Brian K]

Yes the tank is bad. But that may not be the only problem. Usually the electronics in those MQ pumps fail, which causes the pump to cycle on and off a lot, which will wear out a tank diaphragm. Your real fix and something that will last 30-40 years looks like this.
View attachment 58928

Thanks for the info! I too have a MQ that is short cycling. 11secs on, 20 off. Replaced flow sensor. Same deal. Before I sink more money into a tank or pressure switch for it, I have this question. Can the MQ act as the pump in your above Pside kick picture, if you bypass the control board and just use the motor? Or do I need to buy a new pump too? Thanks for any input!

 

[Valveman]

It is not that that pump won't work with a CSV, that pump can't build enough pressure to work with a regular pressure switch. The MQ uses the flow switch to shut the pump off when flow stops, instead of building up more pressure and hitting a set point on a pressure switch. Just have to check how much pressure that pump can build. But you really need a jet pump, as the jet makes it build the pressure needed for the pressure switch. Jet pumps are more expensive, which is why they use those type pumps and the flow switch. But jet pumps are bullet proof, and you see what happens when you try to use electronics instead of mechanical solutions.

 

[ColdMainer]

Hello everyone,

I purchased a house that had a MQ3-45B pump installed in line with the main city water. Within the last few months I have noticed that pumps cycles on and off repeatedly, but it doesn't do it every time. I believe I have narrowed it down to the cycling occurring after small water draw offs. After doing a little bit of research and speaking to a few people it seems like the problem might be the take up pressure bladder being under inflated.

I turned off the main water supply and unplugged the pump then drained the lines. I then knocked off the back cover and unscrewed the bladder/pressure tank (Part Number: 96565367). Water continued to drain out of the pump as well.

I unscrewed a little cap from the top of the bladder/pressure tank to expose what looked like bike valve. I was told to inflate the pressure tank to roughly 25 psi. Unfortunately I can't get the tank to take any pressure. I have tried a bike pump and a small compressor (the type found in a battery pack you would keep in your car). When I use a pressure gauge to try and check the pressure from that valve, I get no reading at all.

The tank seemed to have water in it so I shook it to try and get out as much of it as possible and tried again. The tank still will not take pressure. When I hook the compressor up to it and set it for 25 psi it immediately cuts off.

Is there something that I am missing or doing wrong? Is this bladder/pressure tank bad?

Thanks!

I've got the same thing going on right now. My small pressure tank on the back of the grundfos was full of water, wouldn't take any air when applied. Parts are scarce do to it being discontinued.

My system consists of a radon water filtration system. I bought a new countyline 1 hp water pump. The thing goes berserk when I start it. I guess I'll have to cough up the extra $$$ and buy one of these PSIDE kick systems to hook up to itm

 

[Valveman]

I've got the same thing going on right now. My small pressure tank on the back of the grundfos was full of water, wouldn't take any air when applied. Parts are scarce do to it being discontinued.

My system consists of a radon water filtration system. I bought a new countyline 1 hp water pump. The thing goes berserk when I start it. I guess I'll have to cough up the extra $$$ and buy one of these PSIDE kick systems to hook up to itm

Yeah the PK1A will make any jet pump purr like a kitten and deliver strong constant pressure without cycling the pump to death.