Water pump cycles on and off?

[acritzer]

Just replaced my water pump. It's a shurflo 4008 I think. It cycles on and off when I turn on a faucet, water flow is fine, but the pump constantly turns on and off...about 1 sec between each.
This did not happen with the old pump so I'm assuming the plumbing is all ok. Do I need to adjust the pressure setting screw? I've read that if I back it out a bit (counter clockwise) I can fix the cycling.

Is this an Allen wrench screw?

[DiskDoctr]

We just got back from a week plus and our pump did the same thing- at very low flow rates (barely turned faucet on), and it ran continuously when open further.

When trying to conserve battery and reduce all sound, constantly on and off does not meet our goal. Great flow, though.

We'll be adding an accumulator and replacing some hard lines with flexible and insulating some vibration points.

In our experience, an accumulator is good for a few flushes as well when the pump is off. Imagine coming back from being out all day and having the pump off while you're gone, and sneaking into the bathroom and either having to go switch on the water to flush, or if just washing hands, walking through camper with soapy hands, LOL.

Well worth it, IMHO 😉

[acritzer]

doxiemom11 wrote:
While you were working on the pump, did you have your water set up to use from the city water connection. If so, did you remember to change it back for tank and pump use? Our pump does that if we have not changed our handle back to what we are using.

Our trailer doesn't have this feature. I'm going to try the adjustment settings when I'm back home and have my Allen wrenches.

[doxiemom11]

While you were working on the pump, did you have your water set up to use from the city water connection. If so, did you remember to change it back for tank and pump use? Our pump does that if we have not changed our handle back to what we are using.

[georgelesley]

acritzer wrote:

georgelesley wrote:

Old-Biscuit wrote:
Your Shurflo 4008 has TWO adjustments. \\\

One is for pressure switch....
One is for Bypass control

Bypass allows water to return suction side during low water demands

IF you do not adjust CORRECTLY then pressure adjustment and Bypass adjustment can overlap and cause pump to NOT shut down.


HERE is an off-the-cuff adjustment method

Ours did the same thing until this adjustment was done now runs smoothly w/o cycling.

So did you do the entire "reset" adjustment listed in the link?

Yes. Might take a few tries to get it exactly right

[DC_MC]

New pump last year and it cycled too much also. We called Sureflo and they told us to turn the adjustment screw. Can't remember how many turns but it did fix the problem

[acritzer]

georgelesley wrote:

Old-Biscuit wrote:
Your Shurflo 4008 has TWO adjustments. \\\

One is for pressure switch....
One is for Bypass control

Bypass allows water to return suction side during low water demands

IF you do not adjust CORRECTLY then pressure adjustment and Bypass adjustment can overlap and cause pump to NOT shut down.


HERE is an off-the-cuff adjustment method

Ours did the same thing until this adjustment was done now runs smoothly w/o cycling.

So did you do the entire "reset" adjustment listed in the link?

[Sam_Spade]

acritzer wrote:
People saying it's working correctly....I have read in the manual that cycling is bad and shortens the life of the pump?

That is ONLY if it is cycling continuously when it should NOT BE.

It MUST cycle on and off in order to work correctly.

[georgelesley]

Old-Biscuit wrote:
Your Shurflo 4008 has TWO adjustments. \\\

One is for pressure switch....
One is for Bypass control

Bypass allows water to return suction side during low water demands

IF you do not adjust CORRECTLY then pressure adjustment and Bypass adjustment can overlap and cause pump to NOT shut down.


HERE is an off-the-cuff adjustment method

Ours did the same thing until this adjustment was done now runs smoothly w/o cycling.

[acritzer]

People saying it's working correctly....I have read in the manual that cycling is bad and shortens the life of the pump?

[Old-Biscuit]

Your Shurflo 4008 has TWO adjustments. \\\

One is for pressure switch....
One is for Bypass control

Bypass allows water to return suction side during low water demands

IF you do not adjust CORRECTLY then pressure adjustment and Bypass adjustment can overlap and cause pump to NOT shut down.


HERE is an off-the-cuff adjustment method

[DutchmenSport]

If you turn on two faucets at the same time, like the kitchen and the bathroom, I bet it will run constantly.

All that is happening is the water pressure is reaching it's max pressure and turning off the pump. Then when water runs, pressure lowers, and the pump turns back on.

Unfortunately, it only take about a 1/4 cup of water for the cycling on-off-on to occur, as there is no give in the lines at all.

The pump is doing exactly what it was designed to do. Chances are, the threshold between on and off and on is much less than on your old pump. As DrewE stated above, and accumulator tank will cause the cycling between on and off to be longer.

Your pump is doing exactly what it's suppose to do. It's fine.

When running my shower, if only the hot water is on, the pump cycles on and off pretty fast. Once I get hot water flow, I turn on the cold to create warm water. As soon as the cold is turned on, the pump runs steady.

It runs steady when I flush the toilet. It pulsates at the kitchen sink, unless I turn both hot and cold on full.

Your pump is fine.

[Sam_Spade]

acritzer wrote:

This did not happen with the old pump

What DID happen with the old pump ?

As mentioned, your new one probably is a higher capacity and the duty cycle will be different.

Also it may make more noise than the old one so you just notice it more.

[DrewE]

Cycling just means that you're using less water than the pump can supply. It could be that it's higher flow than the previous pump, or because the flow is limited by the faucet valve not being open all the way, the aerator being partly plugged, or what have you.

An accumulator tank will not prevent cycling, but will make the period longer and thus less annoying (i.e. several seconds on, several off, rather than once per second). It will also smooth out the pulsations in the water flow some, or at least make them less obviously noticeable.

[phays]

I would try backing the screw out but count the turns or partial turns so you can put it back where it was if you need to.

The pump manufacturer usually says you have an obstruction in the line but my new pump does exactly like you say while my old pump did not. My pump is hard to access so right now I'm living with it.