Flojet pulsing during the shot

[noidle22]

So I have a 2 group Boema that I'm building onto a small cart for events and am using a small Flojet diaphragm pump for supplying water pressure.

This works well for filling the boiler but whenever I try to make coffee, the resulting pressure behind the coffee puck is enough to make the Flojet think there is no flow of water so it cuts off. After a second or so when the inboard rotary pump is unable to sustain the shot and drops a bit in applied pressure, the Flojet kicks back in briefly, upping the pressure and switching back off. The rotary pump drops off, Flojet kicks back in and etc. etc. until the shot is done.

This doesn't appear to affect the appearance of the shot and it tastes fine but it's definitely not right.

Is this just a matter of using a different Flojet which has an adjustable pressure switch or perhaps using an accumulator tank to smooth the pump delivery? The accumulator is about $50 which is much less than a new pump.

It could possibly be the Boema at fault too as they use their own sort of PLV on the rotary pump inlet. I may call Boema and ask them about its exact workings which could provide some hints.

[TC]

The flojet is designed to provide mains pressure and is a peristaltic pump, so some variation can be experienced. If your pump is calling for more water than the pump can supply, I guess you'd experience the behaviour you are seeing. Check pressure at the group and adjust your pump bypass if required. An accumulator tank as you have suggested is an easy fix.

[kaanage]

Do you actually need the Flojet? I've seen plenty of setups where the rotary pump draws directly from a tank/bottle (and fills the boiler as well as providing pressure for shots)

If so, the accumulator tank sounds like a no brainer.

[TC]

Do you actually need the Flojet? I've seen plenty of setups where the rotary pump draws directly from a tank/bottle (and fills the boiler as well as providing pressure for shots)

If so, the accumulator tank sounds like a no brainer.

Yes- it generally depends on the pump. Some don't like water at zero pressure. Where a tank/bottle are employed, a non return valve is essential.

[MrWhite]

I've just been through the process of hooking up a GS3 to a flojet. I initially had the same pulsing issue and a small accumulator solved the problem. An easy fix.

[noidle22]

Ok great, accumulator it is. It's not a flow rate issue, the flojet I have can supply 6lt/min.

I've built a San Marco onto a cart which worked fine on a tank with no external pressure. It's just the way the Boema have their pump inlet built, there's some sort of pressure valve that I think needs a certain amount of pressure to open the valve and feed the pump. I rebuilt one the other day and there's an OPV looking spring/piston setup in there. Boema call it a "water charge" unit.

I'll grab an accumulator and hope it works. Do any site sponsors sell them?

[MrJack]

What about a pressure regulating bypass valve (like an OPV) around the flowjet (i.e. from flowjet discharge back to the tank? Should stabilise the pressure and permit the flowjet to continue pumping even whilst the rotary pump flow is very low.

Whenever the flojet flow is greater then the rotary pump flow, it is just returned to the suction.

Common practice in industrial pump circuits.

Obviously won't help if the rotary pump is trying to flow more than the flowjet (but that would just be inadequate system design)