Watermaker LP pump requirements - any expertise please?

Vas, you need a low pressure gauge to measure the low pressure water your HP pump gets. If it drops you need to fix it as low pressure will also mean low flow. The problem is it can lead to cavitation damage in the pump or low output over the membranes, note, over them, not through them. They need a high flow over them to keep them clean and your flow meter (is the name) won't show this.
 
  • Like
Reactions: vas
I have a bypass on my lp pump and a guage to indicate pressure.
I also have a fan on the lp pump to cool it a bit.



vas said:
if I may reward and ask again a question not clearly answered earlier in this thread:

how do I know if my HP pump is starved for water?
I assume that since it does the specified water output I'm fine.
I don't have a LP pump, and other than starting I don't see any bubbles on the lph vertical sight thing with the steel ball in it (guess there's a proper name for it...)

I do get output jumps (starving/overpressure/resetting) of the pump only when filters are blocked or if I'm doing more than 7kn while w/m is running.

cheers

V.
Click to expand...
 
  • Like
Reactions: vas
thanks guys!

Easy to add a tee and measure at the filter output before going to the HP.
Coming to think of it, my HRO w/m does have a sensor on the filter housing output side (will check tomorrow) so maybe the controller does check that before accepting and turning on the safewater indicator.
Do we have any recommended value for that? I guess we are talking vacuum if I don't have a LP, no?

cheers

V.
 
Hm, just checked the manual, my WM3015C pump is 3GMP and rated inlet pressure is from -5 up to 50psi
And there is a low flow switch (or low pressure depending on model will check tomorrow) on the filter housing.
Testing actual values with a wika gauge wont be bad anyway so will do tomorrow!

edited to add that a CAT277 rates input pressure from floaded up to 60psi, so slightly different to mine that seems to accept negative values.
I wonder though if by inversting in a decent 220V impeller pump I'm going to save the pump in the long run and have higher production.

cheers

V.
 
Last edited:
sailaboutvic said:
If your LP pump wasn't keeping up with the HP pump you soon know , you be sucking up air ,
Click to expand...
well that's the point, I don't have a LP pump and HP doesn't seem to be sucking air (but doesn't look there's an failproof and easy way to establish that)
HP pump below waterline (just)
 
If your using. At 247 or 277 pump , it won't be man enough to suck up water even if it's below sea level , it needs to be feed.
you have to remember you will or should had two pre filter before the pump , has explain to the OP a puppy impeller pump will do the job without any problems, no disrespect but I keep going through this , info I am given comes with four years experience using one with a Cat 277 , it not some thing I am google up and posting what I googled without knowing if that pump will work or how long for .
Yes I sure there other LP pump that will do the same job BUT it you don't want to waste money on buy one to find it won't then the answer is above.
The LP pump is used to bleed air from all the components between the intake through-hull and the inlet side of the high-pressure pump. It Another reason to use a LP pump.
the Jabsco Water Puppy (impeller type) are self-priming and can be mounted above the waterline but require the impeller to be checked .

centrifugal type are not self-priming and must be mounted below the waterline .
Hope this help
 
Reading about watermakers at first I didn't realise that there were two approaches to getting pressure to 800psi. Useful to point it out here. If you have varying speed of the pump (eg run from an engine) you need a pressure regulator. If running from a constant speed (a motor) you can use a much cheaper needle valve. It took me some time to realise the difference and others may have the same problem.
 
dgadee said:
Reading about watermakers at first I didn't realise that there were two approaches to getting pressure to 800psi. Useful to point it out here. If you have varying speed of the pump (eg run from an engine) you need a pressure regulator. If running from a constant speed (a motor) you can use a much cheaper needle valve. It took me some time to realise the difference and others may have the same problem.
Click to expand...
You can run from and engine and use a needle valve. You simply have to set the engine revs to the correct speed of the watermaker pump. I know several boats that have this system
 
geem said:
You only need a bypass if your LP pump is a positive displacement pump. If you use a centrifugal pump you dont need a bypass
Click to expand...

Yes, that's what I used. Wasn't sure of final location when I was getting all the bits so that was best option. It ended up being a few inches above the waterline with the inlet trap higher still.

The bypass is useful, though, because I can alter the supply pressure to the HP pump.
 
geem said:
You can run from and engine and use a needle valve. You simply have to set the engine revs to the correct speed of the watermaker pump. I know several boats that have this system
Click to expand...

Does that mean you either run system at anchor or at a single speed underway? Not so flexible.
 
dgadee said:
Yes, that's what I used. Wasn't sure of final location when I was getting all the bits so that was best option. It ended up being a few inches above the waterline with the inlet trap higher still.

The bypass is useful, though, because I can alter the supply pressure to the HP pump.
Click to expand...
If you have a centrifugal pump you dont need to alter the supply pressure. The pump will ride its curve automatically. So if the pressure it is pumping against is high it will automatically reduce the flow. Centrifugal pumps that can develop good pressure are useful as LP pumps as they can deal with dirty filters. If the filters are dirty they create a high pressure drop that can reduce the intake pressure available to the HP pump and in the extreme they could allow cavitation at the HP as the inlet pressure would be low enough. If you can mount the LP below the waterline then a centrifugal pump is a far better solution for its simplicity and robustness
 
geem said:
If you have a centrifugal pump you dont need to alter the supply pressure. The pump will ride its curve automatically. So if the pressure it is pumping against is high it will automatically reduce the flow. Centrifugal pumps that can develop good pressure are useful as LP pumps as they can deal with dirty filters. If the filters are dirty they create a high pressure drop that can reduce the intake pressure available to the HP pump and in the extreme they could allow cavitation at the HP as the inlet pressure would be low enough. If you can mount the LP below the waterline then a centrifugal pump is a far better solution for its simplicity and robustness
Click to expand...

Very interesting. I have a small plastic needle valve thingy which lets me change pressure to set at around 10psi.

I built mine by just trying to reverse engineer an existing system so was not really aware of all the different design choices and the reasoning. However it works well, so happy enough.
 
Goldie said:
The LP pump fitted to my watermaker has failed irreparably, but causes no immediate problem as I've fitted the 'like for like' 20 year old spare which the previous owner had left with the boat and so far, it's working fine - but, it is 20 years old..... I would now like to replace the spare but the pump in question (12v Stuart Turner CH4-14-DC12) is no longer produced. What I'm trying to identify is a currently available, suitable pump. There is a thread on 'Liveaboard Link' regarding watermakers and without wishing to hijack the thread I did raise the question and a couple of Forumites kindly responded that they use Jabsco Water Puppy pumps. Before I order one though, I'd like to make sure that this is indeed suitable for my installation.

The 'old' Stuart Turner is rated at max working pressure of 5 bar and with a flow rate of 62.5 l/min at 0.5 m head and I've found nothing comparable to that spec to date. The question I ask then, is what does the system actually require from its LP pump? What flow rate and pressure? Any other factors to consider? The HP pump is a Cat 277 (engine driven via belts) and has an output (from the manufacturer's website) of 16 l/min. The system runs through 3 pressure vessels/membranes, each of approx. 25 inches in length and fresh water output is on the order of 80 l/hr. The LP pump is mounted below waterline level and the HP pump roughly at waterline level so no significant head is involved.

Any knowledgeable guidance as to what is actually required from the LP pump would be very much appreciated. The company which originally manufactured the system have moved away from watermakers and frankly, aren't interested in advising.

Many thanks in anticipation.
Click to expand...
Which part of the pump has failed? If its the motor you could send it off to be refurbished. When the LP Shurflo pump on my watermaker failed I sent it off to Electric Motor Repairs, armatures, London, Rewinds, Robson and Francis and they refurbed the motor. Now it works perfectly! It cost £160 which was much cheaper than buy a new replacement from Spectra in the USA
TS
 
tudorsailor said:
Which part of the pump has failed? If its the motor you could send it off to be refurbished. When the LP Shurflo pump on my watermaker failed I sent it off to Electric Motor Repairs, armatures, London, Rewinds, Robson and Francis and they refurbed the motor. Now it works perfectly! It cost £160 which was much cheaper than buy a new replacement from Spectra in the USA
TS
Click to expand...

Thanks TS. It basically disintegrated internally! I’ll contact them with pics but I think it’s a lost cause. I’m going to take the advice of VicS and use a Water Puppy.
 
You must log in or register to reply here.

Share this page

Top