Shur-Flo water pump quick question

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Moderator Emeritus
Feb 9, 2013
Minneapolis, Minnesota
It's working fine, except it runs in "bursts" when faucets are turned on. With the toilet, it runs steady.
I thought there was a previous topic about this but cannot find it. If memory serves, there is an allen wrench adjustment screw somewhere to adjust this so it runs steady?
The toilet uses more water (gpm)  than the sink faucet.  The pump goes one speed.  Since the toilet can use all the water the pump can furnish, it runs steady on.  The faucet takes less water.  The pump runs until the high pressure limit is reached, and shuts off.  As water continues to run, pressure drops to low limit and pump kicks on.  Repeat.

In theory, this will not hurt the pump.  If it bothers you (it did me), install an accumulator tank.  It "buffers" the pressure to reduce cycling.
Normal operation.  The water flow for the toilet (And likely shower) is high enough the pump can just keep up with with The sinks the pump is "Faster" than the faucet so when ther pressure builds the pump shut off.
The pressure shut-off is adjustable on most pumps, but that's not your problem (as others have explained).  Try opening the faucet further - the rapid cycling should slow or stop.  If it doesn't the faucet may be clogged with mineral salts.

Other than an accumulator, the pump could be replaced with a [more expensive] variable flow rate model. Those reduce the cycling by varying the water volume to match demand. Not perfect, but it helps.  Shurflo makes the Smart Sensor variable models, but the most preferred variable pump is the Aquatec.
If you have a Surflow 4048 pump it is a bypass pump and is adjustable and an accumulator is not needed with that pump.  Pumps will cycle on and off if you don't open the faucet enough.  With the faucet running slowly the pump is apple to reach it's shutoff pressure.  Because the water is running the pump drops to it's start pressure and back on it comes... On and Off surging.  The bypass pump, if set correctly, bypasses water internally not allowing the pump to reach it's shut off pressure so soon thereby allowing you to run the water more slowly with no cycling. This pump has two adjustments.  Long story short, the best way to set it up is by adjusting the center Allen screw (pressure adjustment screw 5/64 Allen wrench). 

With the pump switch "On" and all faucets closed, turn the center Allen screw, on the pump head, counterclockwise until the pump runs.  No water is running, the pump is just bypassing internally. Now turn the screw the other way until the pump stops running and give it a little more turn after the pump stops bypassing.  If you try to adjust it down too much the pump may not stop running when you close the faucet (continues bypassing). The problem I have found with this pump is that they are voltage sensitive.  If you set it up on battery voltage so that you can run the water very slowly without cycling then the pump may not shut off when you close the faucet while on shore power.  The answer is not to try to get it set to where you can run the faucet too slowly without cycling.  Set it a little higher and it will work satisfactorily on city, battery and generator electric power. There is a second adjustment screw at the lower left of the center screw.  This is the bypass adjustment.  It's best to leave that one on the factory adjustment as you can really get out of sync if you adjust both screws.  If you do get out of sync here is how to get back to the starting point:

Use the following process to adjust the shutoff and bypass pressures: (This is for the 4048 Surflow pump)? Remove the pressure adjustment screw completely, mark the screw in relation to the switch housing for reference as to number of ?turns?. Start screwing the set screw Clockwise ?9 to 9-1/2 turns?. This will increase the pressure to shutoff at approximately 55 PSI.? Remove the bypass adjustment screw completely, mark the screw in relation to the bypass housing for reference as to number of ?turns?. Start screwing the set screw Clockwise ? 14 to 15 turns?. This will increase the maximum bypass pressure to approximately 65 PSI.
Change To:

Sometimes minerals or debris will clog the aerator screen in a faucet, reducing the flow rate.  On most faucets the aerator valve unscrews so you can clean the screen.

If the aerator is stuck, try turning it with a pair of pliers gripping through a jar opener pad to avoid scratching the faucet. 
I've taken your advice and removed the aerators from the faucets. Visible mineral deposits. I have them soaking in lime / calcium remover overnight.
We'll see if that helps.
I'm trying to get the model number of the pump, but it's hidden from view in the compartment. A telescoping mirror should help.
Thanks again
I'm soaking the aerators one at a time.
Good grief.. I thought I was on top of most maintenance.
Hopefully this might solve the problem.


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