Pump hammering after installing accumulator

[obscenic]

I have a class B with a nearly new pump (Shurflo 4008, installed about 1 year ago). Even with the bypass, running the sink caused pump cycling to a degree though not as bad as it was with the old 3 chamber pump. I decided to add a small accumulator to smooth out the flow and reduce cycling; even though I know the bypass and the accumulator both are designed to accomplish the same thing.

Now, when running the sink (even at very low output) the water flow is smooth and the pump cycles normally and acceptably. However, occasionally when you turn the tap off, the pump hammers on and off for about 1-1.5 seconds quite loudly. It probably cycles 7 or 8 times until it hits pressure and shuts off.

I'm wondering what I could do to correct this, and if anyone can assess what the cause may be. Thanks in advance!

[Hurricaner]

I have a 4008 with a 1 gallon accumulator, installed it about 2 years ago. It worked fine with the factory settings. I believe I had the accumulator Air pressure set for around 25 psi. The only problem I have is when I get air in the system and that was a problem with the old shurflow.

Sam

[obscenic]

Jetstreamer wrote:
I had the exact problem and surmised that the bypass type pump does not interface well with an accumulator tank. I spent a lot of time messing with the pressure set screws on the pump and could not get it to work well. I think the accumulator somehow interferes with the way the bypass feature tapers off the flow of water/pressure....
Ended up replacing the pump with one of the older style non bypass types and it works great. I wouldn't be without the accumulator setup..
I'm sure that your hammering issue may stem from the fact that the pump isn't quite cycling correctly and you may have an additional problem with water lines rubbing somewhere...
Just some thoughts from personal experience....

Interesting, I suspected this was the problem, but I didn't find any posts about this online so I wasn't sure. This sounds exactly correct. I'm on city pressure for the meantime, but I'll have to swap back to the old style pump I suppose.

Old-Biscuit wrote:
Shuflo 4008 bypass SHOULD start to open at 40psi

Bypass adjustment is screw in assembly down low and closer to inlet side

Pressure switch adjustment is screw in assembly with wires coming out

Increase set points.......turn set screw 'CLOCKWISE'
Decrease set points.......turn set screw 'Counter-Clockwise'

Bypass should start to open at 40psi....fully open at 65psi
Pump shutoff should be at 55psi


Caution:
Full by-pass pressure setting should be at least 10 psi higher than pump shut off pressure.
If full by-pass is reached before the shut-off setting, the pump will not shut off.

So, if I understand correctly, if I fully turn the bypass adjustment (get it way up over 70PSI or so), it should eventually just never open at all because the pump will shut off before the line sees that much pressure?

[Jetstreamer]

I had the exact problem and surmised that the bypass type pump does not interface well with an accumulator tank. I spent a lot of time messing with the pressure set screws on the pump and could not get it to work well. I think the accumulator somehow interferes with the way the bypass feature tapers off the flow of water/pressure....
Ended up replacing the pump with one of the older style non bypass types and it works great. I wouldn't be without the accumulator setup..
I'm sure that your hammering issue may stem from the fact that the pump isn't quite cycling correctly and you may have an additional problem with water lines rubbing somewhere...
Just some thoughts from personal experience....

[Old-Biscuit]

Shuflo 4008 bypass SHOULD start to open at 40psi

Bypass adjustment is screw in assembly down low and closer to inlet side

Pressure switch adjustment is screw in assembly with wires coming out

Increase set points.......turn set screw 'CLOCKWISE'
Decrease set points.......turn set screw 'Counter-Clockwise'

Bypass should start to open at 40psi....fully open at 65psi
Pump shutoff should be at 55psi


Caution:
Full by-pass pressure setting should be at least 10 psi higher than pump shut off pressure.
If full by-pass is reached before the shut-off setting, the pump will not shut off.

[ScottG]

It may be as simple as a line up against a wall or other hard surface someplace. That can make a tremendous racket. A bit of pipe insulation will stop it.

[Hurricaner]

Air in the lines. Try opening the faucet all the way after you fill the tanks a let it run for 30 seconds or so.

sam

[Harvard]

My pump hammers when it sucks air in water which happens if and when I let the fresh water tank to go dry. The reason for air in the water, AFTER I refill, is because my inlet to the pump has an air trap in the piping.

[RJsfishin]

That type bypass pump doesn't need any bladder tank, let alone a bigger one.

Having said that, mine works great w/ the little bladder tank,.....once I adjuster the bypass correctly.

And having said that, the 4008 is a cheap universal pump that works well for most I guess.
But I have had too many problems w/ mine, like the screws coming loose, until I installed lock buts on 3 of the 4 bolts. Then I had trouble w/ overheating and shutting down when ever using very low water flow. I finally removed the internal thermosistor, and no more problems.

But if I needed a pump, it sure would be a higher quality than the 4008.

[brulaz]

Trackrig wrote:
I'm not sure what you mean by a bypass pump? I'm using the Shurflow pump that was already in the MH's water system.

Bill

The 4008 and others have an internal bypass valve that allows it to maintain pressure without cycling on/off. Sometimes, at certain flow rates, it can be quite noisy.

With ours, it only gets noisy when running cold water. The 6g hot water tank seems to buffer it when pumping hot water. My guess is that the OP would be better off with a bigger pressure tank.

[RJsfishin]

If the 4008 pump keeps running slowly after the pressure is up, I can't believe it didn't have the same problem before you installed the bladder tank.
The problem is common on that bypass type pump, and is easily corrected by adjusting it, by turning a little allen screw. There are 2 of them as I remember, one being the on/off pressure adjustment, the other being the bypass pressure adjustment, which is the one that needs adjusting.
You can trust me on this because I been down this road when I first bought my 4008. I installed it, and it wouldn't completely shut off. I went back to the dealer w/ the problem, and they didn't have the foggiest idea, so they called shurflo, and they right away said to turn the allen screw 1 full turn (don't remember which way) to fix the problem, and they were very correct. I would hope one of the techs here could tell you the exact location of the screw, as I don't remember 3 years ago, but I do remember it is near where the wires connect

[Trackrig]

I'm not sure what you mean by a bypass pump? I'm using the Shurflow pump that was already in the MH's water system.

Bill

[obscenic]

Trackrig wrote:
The two most common accumulator tanks are the littler plastic one and the larger steel one. I installed the larger one in my MH and all has been fine with it. I'll install another larger one in my TT in the spring when it's warm outside again.

With the larger ones you have to set the air pressure in the bladder. In the four years it's been installed, I've had to re-pressure the bladder once. Does the smaller one also need to be pressurized and did you do it?

Bill

Small plastic. Do you also use a bypass pump? My accumulator was factory pressurized and I checked the pressure and it's good. You can feel it working, you get a nice steady stream when the pump turns off.

[ROBERTSUNRUS]

🙂 Hi, if your pump continues to cycle, you might have a small leak somewhere or air in the lines. If you haven't already done this, I would suggest that you install flex hoses to the pump.

[Trackrig]

The two most common accumulator tanks are the littler plastic one and the larger steel one. I installed the larger one in my MH and all has been fine with it. I'll install another larger one in my TT in the spring when it's warm outside again.

With the larger ones you have to set the air pressure in the bladder. In the four years it's been installed, I've had to re-pressure the bladder once. Does the smaller one also need to be pressurized and did you do it?

Bill