Booster Pump causing supply pipe to jerk

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AWalt

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Hi, I’m using the MQ3-45 on a 3/4” main with City Water. It works great so far; except that when it kicks in the inlet pressure gauge, drops all the way down for a split second and the pipes jerk. Would a vacu-arrest: Vacu-Rester 1/2" MIP Vacuum Breaker Water Hammer Arrestor eliminate this issue? There is no lag or decrease in water flow when this happens. I’m concerned about the supply connections which are buried behind a gas fireplace. I know this was not a smart thing to do. My supply pressure is about 45 psi (a little high) and I will probably add a regulator as I did for the output. I keep the pressure at about 65psi. Any suggestions would be greatly appreciated. Been using the pump for six months for house and irrigation. No issues except for the thud:)
 

Valveman

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Well the "thud" is a pretty good issue! Those pumps are known to cause problems and not last very long. Here is a picture of a Dumpster full of MQ pumps, which is where I mostly see them.
IMG_0003.JPG
 

Valveman

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Anyway, your thud problem is probably caused by the internal tank in the MQ pump having to little or too much pressure. That little internal tank only holds a couple spoons full of water. The tank is supposed to supply water until the pump gets up and running. The air pressure in the tank needs to be a little less than the start pressure of the pump to make that happen. Many people just add another regular pressure tank, as the one in the MQ pump isn't large enough for anything. Since you are adding a pressure tank anyway, might as well add a good pump like a regular jet pump. Grundfos makes regular jet pumps in the JP series. Then you could control it with a Cycle Stop Valve and have something that will deliver better pressure than the MQ and last several times longer. It would look something like this.
PK1A on jet pump.jpg
 

AWalt

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Sounds like everything needs to be finely tuned to prevent the jerking that's happening in my situation. The pump works great however and provides good constant pressure. I'm only concerned that it's making the pipes about twenty-five feet away from the pump where the main enters the house jerk a bit. I do have an expansion tank on the upstream side for the hot water heater. It's only a few feet away from where the pump is. Are you saying I should install one on the down streamside as well? They're fairly inexpensive. Thanks a lot for your reply!!!
 

Valveman

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Your expansion tank should work. But you will need to reduce the air charge in the tank to 5 PSI less that where the pump starts. Sure those pumps work great until they don't. But on Christmas day or some Saturday morning there will be no water coming out of the faucets and you will be looking for a better alternative. That "thud" is a water hammer that is sending a 500 PSI spike through your plumbing system.
 

AWalt

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Hi, Thanks again. This is such a tricky problem. I'm on City Water and when the pump is off the lines just decrease to the base pressure through the pump. It's low, about 40psi or so. I put the pump in to improve our shower experience. I also have a bypass if I have to remove or work on the pump. The regulator after the pump is set to 65psi. There are about twelve feet of 3/4" pipe between the pump and the 4.5-gallon expansion tank.

Just to clarify, do you think the existing tank set to 60psi might solve the problem? Or should I add another tank at the supply side at 35psi? Also, the supply side pressure fluctuates by about 5psi.

I think you're right about going with a different pump down the road. All the reviews show how unreliable these are.
 

Valveman

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Hi, Thanks again. This is such a tricky problem. I'm on City Water and when the pump is off the lines just decrease to the base pressure through the pump. It's low, about 40psi or so. I put the pump in to improve our shower experience. I also have a bypass if I have to remove or work on the pump. The regulator after the pump is set to 65psi. There are about twelve feet of 3/4" pipe between the pump and the 4.5-gallon expansion tank.

Just to clarify, do you think the existing tank set to 60psi might solve the problem? Or should I add another tank at the supply side at 35psi? Also, the supply side pressure fluctuates by about 5psi.

I think you're right about going with a different pump down the road. All the reviews show how unreliable these are.
You need a check valve before the pump. The pressure should not drain down to city pressure when the pump shuts off. The kind of pump you have is the problem. The pressure regulator after the pump is another part of the problem. The pump controls should control the pressure. The MQ just runs full out and adds its max pressure to the 40 PSI you have coming in. Some people put the pressure regulator on the inlet side of the pump. Reducing the pressure to the pump to 10-15 PSI also limits the max pressure after the pump as it can only add so much. Having the pressure reducer after the pump means you need an expansion tank after the PRV. So, you would need another small pressure tank before the PRV with less air charge than the on pressure of the pump.
 

AWalt

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The pump has a check valve. The water only flows one way. The check valve does not stop water from flowing through the pump into the house when the pump is shut down. It can’t flow back. Of course in that situation the pressure would only be what the city pressure is. My problem is on the “low pressure” supply side. The torque on the pump is pulling to much water on kick in. The water on the upstream side of the pump remains pressurized when the pump is off at 65 psi when the pump is powered. Does that make sense?
 

SHEPLMBR

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A big reason we have found that these fail is because of installation error. They should have a prv installed before and the pressure needs to be lowered many times.
 

AWalt

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That may help. Sounds like the supply line is too small for how much the pump puts out at start up.
I think that may be the case. It just can't move the volume of water immediately. The main supply is only 3/4"
 

AWalt

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A big reason we have found that these fail is because of installation error. They should have a prv installed before and the pressure needs to be lowered many times.
Thanks. I'm right on the cusp of the maximum input pressure is for the pump. I think I'll bring it down to around 35psi. I wonder if that will help with the kick-in issue as well.
 

Valveman

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It might make it worse as it would be further starving the pump. I would go PRV, small pressure tank, then pump.
 
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