Plumbing problem...

I read this whole thread, and several others I've found on pulsing/cycling pumps.

Half-way through this season, the ShurFlo 4 GPM potable water pump I installed last summer started cycling or pulsing rapidly when any faucet was used. It pulses on/off a little faster than once per second.

The manual claims no accumulator tank is needed, and so I didn't install the one I bought, mostly because it will take a significant bit of plumbing re-work.

The manual says "The pump operates normally up to about 30-psi [2.06 Bar], where a spring-loaded by-pass valve opens, allowing flow back from the output side to the input side, providing smooth, steady flow with virtually no cycling, all the way down to a trickle. As a faucet is opened back up, the pressure will drop, the by-pass will close and full flow is again obtained. This allows good flow, even with today's restrictive showers and pullout sprayer faucets."

So, why did it start cycling or pulsing all of a sudden?

My first thought was that the above is all BS, and I really do need to install the accumulator. Maybe my hot water tank was acting as an accumulator until the last bit of air at the top of the tank finally made its way out into the lines or was absorbed into the water.

My question is: Is this a normal failure mode for these pumps? Maybe adding the accumulator won't help.

I think you've got a problem with the by-pass valve. If the by-pass fails the pump becomes just a regular dumb on and off pump and would cycle as you've described. If the pump is still under warranty, take it back to the dealer. If it's out of warranty, call ShurFlo and see if they can give you help in fixing it. Of course the third option is to do what I would do. Take it apart, be unable to put it back together, and buy a new one.

Sounds like it is broken. These pumps are somewhat famous for having this problem. Hopcar is right give them a call they are usually helpful.

I called ShurFlo. Spoke to a native English speaker right away. She suggested turning the set screw in (clockwise) on the bypass valve one complete turn.

It worked. The pulsing has stopped, and I get a steady stream down to a trickle (at which point it cycles again, but that's OK.)

Thanks for sharing that. Now if one of my customers has that problem I'll know what to suggest. I always learn something useful on this forum.