HRO Watermaker problem

[Clockwork575]

Hi
I was wondering if anyone could help. Ive got a Seafari Mini 750 watermaker and it keeps showing ID3 "Low water pressure" on the income side. Ive changed the prefilters, the strainer and pulled apart the booster pump - which all seems fine. I cant measure pressure or flow aboard although when I start the booster pump it reads over 10Psi on the panel but as soon as the high pressure pump starts the inlet pressure drops down to almost vacuum (0 Psi).
Ive just about tapped-out with frustration and exhausted my rudimentary knowledge.
I will have to head in to Bodrum to try and get it fixed if I cant figure this issue out.
Thanks in advance.

[a64pilot]

First check that your thru hull and strainer are clear, you may have a jelly fish or something stuck in the thru hull itself.
What you describe matches exactly to they way a restricted inlet presents. Not saying it is, but it’s where I’d start

[GordMay]

Greetings and welcome aboard the CF, Clockwork.

[Clockwork575]

Thanks, I did try that and its all clear. Ive followed everything through to the machine itself and it all seems good.
Can booster pumps achieve pressure (PSI) but not flow when they are worn out? It seems to be fine though.

[Sailmonkey]

Have you tried disconnecting the inlet hose and running the booster pump? Does the flow seem adequate?

What type of pump is the booster? A diaphragm, a centrifugal, an impeller?

[Clockwork575]

Its a centrifugal pump but I havent pulled the outlet off and watched the water flow. The centrifuge looked to be so simple it simply couldnt fail...but Im sure it could. I even pulled apart the non return valve after the booster pump to see if this was clear and working - which it was.

[a64pilot]

It’s tough to get 10 PSI out of a Centrifugal pump, although I much prefer them as they are so simple.
I still think you have a restriction if it used to work, then suddenly stopped. How are you checking?

[Clockwork575]

I sit at the unit itself (watermaker) and turn the booster pump on...there is positive pressure there (but of course I dont know the flow).
As soon as I turn the watermaker on (high pressure pump) the inlet pressure drops away and the machine drops.
I was wondering if it could be a blocked feed line to the low pressure gauge and low pressure sensor (are these fed the same way?).
I also note that the fresh water wash shows to provide plenty of PSI on the low pressure side when its washing.

[Sailmonkey]

I’m convinced it’s either a blockage or a spun vane impeller on the pump shaft

[Clockwork575]

Thanks Sailmonkey, I'll have another crack tomorrow. I will take the inlet hose off right at the watermaker and see if its getting flow and pressure. If not I'll work back to the booster pump checking along the way.

[a64pilot]

Originally Posted by Sailmonkey

I’m convinced it’s either a blockage or a spun vane impeller on the pump shaft

Spun vane would slip more as pressure built wouldn’t it?
Meaning you would get flow, but little pressure, he is having the opposite problem I believe.

But good thinking, I didn’t even consider it cause I didn’t think about it.

[Sailmonkey]

Originally Posted by a64pilot

Spun vane would slip more as pressure built wouldn’t it?
Meaning you would get flow, but little pressure, he is having the opposite problem I believe.

But good thinking, I didn’t even consider it cause I didn’t think about it.

I’m thinking it’s possible the vane could spin enough to generate 10psi, but not able to provide any real volume. But who knows. It could be a dead catfish in the strainer elbow.

[CassidyNZ]

It’s probably too obvious to state that flow and pressure are not really connected. An example: connect a garden hose to a municipal (high pressure) system, turn the faucet on just a little bit then try to pinch off the hose. Even though there is no volume, the pressure will soon build to a point where you can’t hold it back any longer.

With that as a backdrop, it would seem obvious also that the pump can deliver good pressure but poor volume. Whilst I don’t know what pump you have, I can’t say how it can be fixed except that a replacement pump would tell that story beyond dispute one way or another.

Beg, borrow or steal another pump and try it.

[Clockwork575]

So I've pulled the hoses off the booster pump and it seems great. I pulled the inlet hose off the watermaker (after all the filters, strainers etc) and its also great. Lots of flow, lots of water.
So I reconnect the water and turn the booster pump on...again 12 PSI. But as soon as the high pressure motor starts the pressure immediately drops to zero.
However I noticed the low pressure gauge tube is taken off the high pressure pump manifold very "near" the inlet. Seems a silly place to have it as it's reading may be affected by the high pressure pump.
It may be attached here as its right where the water comes into the HP manifold pump and gives the actual water reading at the actual pump - not in the hose coming into it.
Anyway, its really got me beat.

[Sailmonkey]

So you’re registering low pressure with an electronic transducer.

Do you have any sort of mechanical pressure gauge you can mount to verify the electronic gauge is reading correctly?

Or maybe verify that the booster pump continues to operate when the high pressure pump is turned on?

It now appears to be an electronic gremlin (faulty pressure gauge, or opening relay for the booster) rather than restricted flow.