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Old 14-02-2015, 07:09   #16
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Re: Watermaker woes

Oh yes, thanks for the reply to Catchin' Rays in Georgetown, we will try this temperature thing first but will hail you on ch68 if we are stuck

thanks
Richard
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Old 14-02-2015, 07:48   #17
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Re: Watermaker woes

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Originally Posted by berwick View Post
Wow some good stuff to check out this morning thanks! Our latest thought is that the water temperature coming out of the HP is very warm (and this is feeling thru the HP hose)
If things are heating there is unusual friction or adiabatic compression. Water does not compress much when increasing pressure by 800 psi from atmospheric pressure (say lose 0.5% of its volume). This, will cause a very small temperature increase. On the other hand if you compress gases (air) they will lose more than 90% of their volume, hence lots of work turned into heat.

I would be suspicious about gas bubbles in the inlet of the HP pump (which may come from a leak in the hose before or from as a result of vacuum). Have you checked that there is no vacuum between boost pump and HP pump? Is there a vacuum gauge in the inlet of the HP pump?

If there isnt one then you can check that the boost pump is running fine by disconnecting it form the HP pump at the HP pump inlet, and running just the boost pump into a bucket without any back pressure. You measure the flow rate. If it is more than the design feed flow rate then you will not have vacuum when running the whole system. Otherwise you will, and this needs to be fixed.
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Old 14-02-2015, 07:50   #18
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Re: Watermaker woes

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Originally Posted by 1affiah View Post
As Richard and I are not the owners, and he is in communication with SK support, I do not want to get in the middle of that and foul those waters.

Rich B, the pump is the General WM series, same as yours, with 1hp motor. We are now looking at the pump being overfilled and generating too much heat, as the fresh output is quite warm. We will adjust the oil fill level, and measure output flows with bucket. Input temp is approx. 80F.,

Thanks for the help.

Larry
The 1.6gpm pump runs hit baby...like 180degs. Heat or over filling with oil won't cause these symptoms. Its all about confirming the GPM outlet of the pump at pressure to get to the bottom of this. Also....verify that your pressure relief valve is not blowing and venting off the needed flow that should be going into the membrane.
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Old 14-02-2015, 08:14   #19
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Re: Watermaker woes

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would this high temperature be enough to increase the PPM and reduce the output down a third?
Temperature is NOT the cause of the low product water flow. At a given pressure and feed flow, higher temperature will lead to *higher* % of feed flow going though the membrane (hence higher, not lower, product water output).
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Old 14-02-2015, 08:16   #20
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Re: Watermaker woes

Rich, where would we find the pressure relief valve?

Richard
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Old 14-02-2015, 08:54   #21
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Re: Watermaker woes

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Rich, where would we find the pressure relief valve?

Richard
Richard

I believe that Rich is referring to the "High Pressure Bypass Relief" shown in the attached SK schematic.
Attached Files
File Type: pdf SK watermaker layout.pdf (41.7 KB, 39 views)
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Old 14-02-2015, 08:55   #22
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Re: Watermaker woes

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It still puzzles me about the needle valve, it closes firm and the pressure maxes out at 800. Do they have a built in stop? No other pressure regulating devices on the pump or inline.

Thanks,
Larry
That can happen if the pressure relief valve is set to relieve pressure above 800psi. You can actually close the needle valve all the way and not over pressurize the system as a safety device.....but I'd the pressure relief valve is venting early or partially at 800psi, then that could be an explanation for your symptoms.
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Old 14-02-2015, 09:12   #23
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Re: Watermaker woes

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Richard

I believe that Rich is referring to the "High Pressure Bypass Relief" shown in the attached SK schematic.
Absolutely....what happens is that if the relief valve is venting partially early its stealing flow from going through the membrane....and since product water production is Dependant on flow then boom...you lose production and going from 20gph to 8gph sure sounds like an inlet flow issue and NOT a membrane issue.
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Old 14-02-2015, 09:36   #24
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Re: Watermaker woes

Ok here is the latest, we found a small leak in the intake to the pump - fixed that, the water from the pump is a bit cooler but still too warm I think. We measured flow and have 8 oz of product water per min and 21 oz of brine per min on a 2.3 gpm pump. So I guess the pump is toast?

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Old 14-02-2015, 10:13   #25
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Watermaker woes

Quote:
Originally Posted by berwick View Post
Ok here is the latest, we found a small leak in the intake to the pump - fixed that, the water from the pump is a bit cooler but still too warm I think. We measured flow and have 8 oz of product water per min and 21 oz of brine per min on a 2.3 gpm pump. So I guess the pump is toast?



thanks

Richard

How much water is being released by the relief valve?

On edit, if the relief valve dumps into the brine output disregard


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Old 14-02-2015, 11:23   #26
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Re: Watermaker woes

Yikes.....
Based on your numbers of 8oz and 21oz per minute, your 2.3gpm pump is only putting out 0.22gpm. BUT that number could be bogus if some of the pumps flow rate is being vented out of your pressure relief valve and not actually flowing into the membrane.

If this was/is a boost pump supply problem rather than a HP pump problem then your pump would be cavitating like crazy and sounding like it is trying to fly apart. If you are starving your HP pump for flow, the typical symptom I'd that your pressure will bounce around and will not stay constant.

The good news is that a general pump wet end rebuild is easy....and cheap...like $225 for a valve and packing kit..and it is something an average cruise can do himself. So your pump is not toast....it can be fixed it it is indeed in need of a rebuildm
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Old 14-02-2015, 12:25   #27
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Re: Watermaker woes

Have you checked the voltage being delivered at the pump while the system is running?

Can you disconnect the output from the pump so it goes into a bucket rather than the membrane? If so - what is the flow? What is the voltage at the pump when running with an open discharge?

Question for the experts:

Isn't the feed pump output flow / product flow ratio usually around 6.5?

They are reporting about 21/8 or about 2.6 so they need to determine if the decreased bypass flow is restricted by:

- high back pressure on the feed pump output
( a clogged output from the bypass side of the membrane housing would restrict the total flow and thus reduce the product. But, it doesn't seem like it would change the ratio)

- low voltage on the pump

- bad pump

- restricted flow into the pump

You solve this problem like any electrical problem. Trace the water flow and measure the input and output at each discrete unit:
- input to pump
- output from pump
- output from membrane on bypass side (directly from the membrane BEFORE it goes into the tubing)
- output from membrane on product side (directly from the membrane BEFORE it goes into the tubing)
- at the discharge port over the side for the bypass

- voltage at the power source with no pump running
- voltage at the pump connection with no pump running
- voltage at the pump with the pump running
- voltage at the power source with pump running

At some point you find a number that does not match the necessary specs
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Old 14-02-2015, 15:33   #28
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Re: Watermaker woes

Alright that sounds good about the rebuild kit, I'll pass it on. Ref the voltage, the large generator is running at the same time and they have had no voltage issues, but it is a good point and should be checked. The boat in question has moved location and I believe he is in contact with Rich B ref parts. Thank you for all the help, this is what makes these forums so valuable!

Richard
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