Cruisers Forum
 


Join CruisersForum Today

Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 19-06-2018, 08:25   #1
Registered User

Join Date: May 2015
Posts: 11
Water Maker low pressure supply pump

Hi,
I'm having a little trouble to understand the custom made water maker by the PO of the boat. We have two 2.5 x 40 RO membranes and the high pressure pump is a cat pump 277. My concern is the low pressure pump (Jabsco 31620 with pressure switch). First it constantly switched on and off while running, what I didn't like at all. So I bridged the pressure switch and got at nice permanent flow. However, buy some reason that I have not figured out, the supply pump stops working after about 40 min (no matter if I use the pressure switch o not) and only turns on again after some waiting time (overheating?). My question is, if the supply pump has to be on all the time while the water maker is running, or if I can switch it off after air is bleeded and the cat pump may keep sucking water through the shut off low pressure supply pump?
Thanks for any help and suggestions
Uwe
__________________

uweboerst is offline   Reply With Quote
Old 19-06-2018, 08:38   #2
Moderator
 
a64pilot's Avatar

Cruisers Forum Supporter

Join Date: Oct 2013
Location: Albany Ga.
Boat: Island Packet 38
Posts: 26,427
Water Maker low pressure supply pump

OK just using my Cruise RO as an example, first it has no pressure switch, for the reason Iím sure that you discovered.
It runs continuously, and would Iím sure overheat, but there is a neat little plastic bracket that holds a quite powerful little 12V fan to blow air on the motor to cool it.
I think if I were in your position, I might just contact Rich at Cruise RO, talk to him and probably order one of his pumps, with the bracket and fan.
He answers his phone by the way, personally.

Itís my understanding that you never want any HP pump not having a supply of pressurized liquid, itís for this reason that our little Diesels have a low pressure fuel pump to feed the HP pump, cause if we didnít over time the HP pump may be damaged due to cavitation of it pulling even a slight vacuum.
You need the boost pump.

On edit, his system also has a way to recirculate water, I assume so that the pump doesnít dead head so to speak, it has a way to unload the pump a little, I assume to keep the pump from working too hard and overheating.
Maybe you need one of his boost pump kits, to include the recirculating plumbing? He would know.
__________________

a64pilot is offline   Reply With Quote
Old 20-06-2018, 03:41   #3
Sponsoring Vendor
 
Tellie's Avatar

Community Sponsor

Join Date: Oct 2007
Location: Hollywood, Fl.
Boat: FP Athena 38' Poerava
Posts: 3,353
Re: Water Maker low pressure supply pump

The boost pump needs to be checked to make sure it is a continuous duty pump.
Tellie is offline   Reply With Quote
Old 20-06-2018, 04:56   #4
Senior Cruiser
 
Captain Bill's Avatar

Cruisers Forum Supporter

Join Date: Apr 2008
Location: Punta Gorda, Fl
Boat: Endeavourcat Sailcat 44
Posts: 2,711
Re: Water Maker low pressure supply pump

I had the same problem with my boost pump. It was caused by too much back pressure as the pump was trying to put out much more than the HP was taking and the motor was over heating. I rigged a bypass that fed part of the output back to the intake of the pump. This reduced the back pressure and allowed me to adjust the flow to more closely match the requirements of the HP pump. I put a tee in the outlet line and a tee in the inlet line and a simple ball valve in between. I adjusted the ball valve to keep the HP pump intake flooded but with significantly less load on the pump. You could actually hear the difference in the sound of the pump. The HP pump actually requires very little pressure at the intake but the boost pump was capable of putting out a lot more with a restricted output, but if it's too restricted the electric motor tries to keep up the RPM as the back pressure tries to stall it. This causes it to draw more amps than designed and it overheats. The safety thermal switch then shuts it down. The pressure switch normally would have cut the power when the pressure got too high and the motor was overloading, but you bypassed it. Feeding back part of the output to the input solves this problem.
Captain Bill is offline   Reply With Quote
Old 20-06-2018, 06:32   #5
Registered User

Join Date: May 2015
Posts: 11
Re: Water Maker low pressure supply pump

Thank you for your quick and helpful replies!
I have now ordered a water putty pump that will replace the pressure pump (obviously not the right one for this specific duty) that was installed by the PO. I also like the idea of a pressure relieve setup at the low pressure pump. My understanding is, that I theoretically can reduce the pressure at the low pressure gauge that much that the high pressure pump does not draw a vacuum, right? What does your low pressure gauge read when the water maker is running?
uweboerst is offline   Reply With Quote
Old 20-06-2018, 06:42   #6
Marine Service Provider
 
SV THIRD DAY's Avatar

Community Sponsor
Cruisers Forum Supporter

Join Date: Aug 2006
Location: La Paz, Mexico
Boat: 1978 Hudson Force 50 Ketch
Posts: 3,804
Re: Water Maker low pressure supply pump

Quote:
Originally Posted by uweboerst View Post
Thank you for your quick and helpful replies!
I have now ordered a water putty pump that will replace the pressure pump (obviously not the right one for this specific duty) that was installed by the PO. I also like the idea of a pressure relieve setup at the low pressure pump. My understanding is, that I theoretically can reduce the pressure at the low pressure gauge that much that the high pressure pump does not draw a vacuum, right? What does your low pressure gauge read when the water maker is running?
Better cancel that Jabsco water puppy pump order....

About 4 years ago when ITT Jabsco was purchased by Xylem they added a temp cut-out so low to the water puppy pump thats its now unusable in a water maker install like yours. Its now NOT a continuous duty pump. And when a flexible impeller pump stops it completely blocks the flow starving your high pressure pump and causing havoc
SV THIRD DAY is offline   Reply With Quote
Old 20-06-2018, 08:31   #7
Senior Cruiser
 
Captain Bill's Avatar

Cruisers Forum Supporter

Join Date: Apr 2008
Location: Punta Gorda, Fl
Boat: Endeavourcat Sailcat 44
Posts: 2,711
Re: Water Maker low pressure supply pump

Quote:
Originally Posted by SV THIRD DAY View Post
Better cancel that Jabsco water puppy pump order....

About 4 years ago when ITT Jabsco was purchased by Xylem they added a temp cut-out so low to the water puppy pump thats its now unusable in a water maker install like yours. Its now NOT a continuous duty pump. And when a flexible impeller pump stops it completely blocks the flow starving your high pressure pump and causing havoc
My LP pump is a water puppy and that is why I had to rig the bypass. My water runs are a max of 3 hours and it runs for that long with no trouble. I don't have a low pressure side gauge, but my pre-filters are about a foot above my HP pump intake and I can see the water flowing into the system. When the pump used to shutdown after about 45 minutes the cat pump would start making a bunch of noise and I would shut it down immediately. I have considered a simple water pressure switch that would shut down the power to the HP pump in case of a low pressure failure but have not done so. My brine discharge is white polyethylene and I can see when the water from the LP pump starts flowing through it. I always let the LP pump run for 1 minute before turning on the HP pump. The water puppy has not shut down since I installed the bypass. I have a 2.3 gpm HP pump and my commercial duty water puppy is rated at almost 3 times that volume at 20 feet of head. As the pre-filters clog I probably or more, so even then I'm putting more water through the bypass than through the HP pump. The specs for the pump say don't exceed 8.7psi, my guess is if you exceed that it will eventually overheat.
Captain Bill is offline   Reply With Quote
Old 20-06-2018, 08:35   #8
Marine Service Provider
 
SV THIRD DAY's Avatar

Community Sponsor
Cruisers Forum Supporter

Join Date: Aug 2006
Location: La Paz, Mexico
Boat: 1978 Hudson Force 50 Ketch
Posts: 3,804
Re: Water Maker low pressure supply pump

Quote:
Originally Posted by Captain Bill View Post
When the pump used to shutdown after about 45 minutes the cat pump would start making a bunch of noise and I would shut it down immediately.
Yep....every time that happens you are taking life off of your Hp Pump Packing.

Quote:
Originally Posted by Captain Bill View Post
my commercial duty water puppy is rated at almost 3 times that volume at 20 feet of head..
Pump ratings...oh ya...do you know how many pumps we have tested that are no where close to their rating (this one included)...lots. The ratings are all given at Open Suction and Open Discharge so you are lucky to get 2.5-3.0GPM from a commercial duty water puppy in the real world of water maker plumbing.

A good solution that we did 4yrs ago was to install the bypass....it also lets the same pump be used in lots of different install configurations. But we will be changing that design and doing away with the bypass because it also has potential for problems. We will be going go to a constant PSI diaphragm pump. (the pump does not cycle on/off but it's a VFD style that changes pump RPM to match demand). We have been testing it now for two years and it's quieter, uses less power, simplifies the plumbing, and is more reliable than the water puppy approach with a bypass. So when your water puppy dies, that would be a good upgrade option.
__________________
Rich Boren owner of:
Cruise RO Water High Output Water Makers
Technautic CoolBlue Refrigeration
La Paz Cruisers Supply and Yacht Management and Brokerage
SV THIRD DAY is offline   Reply With Quote
Old 20-06-2018, 09:38   #9
Registered User
 
charris's Avatar

Join Date: Oct 2009
Location: West Coast of Mexico
Boat: Hunter, Legend 40.5
Posts: 18
Re: Water Maker low pressure supply pump

Hello Rich. I am having the same sort of problem. Can you share with us the make and model of the pump you have found to do the job? Many thanks
charris is offline   Reply With Quote
Old 20-06-2018, 09:54   #10
Registered User
 
mvmojo's Avatar

Join Date: Mar 2018
Location: www.mvmojo.com
Boat: Robt Beebe Passagemaker 49-10 in steel
Posts: 206
Re: Water Maker low pressure supply pump

My watermaker is 17 years old and has made 10's of 1,000's of gallons of RO water, 33 gallons per hour. Rather than use a separate low pressure pump to supply the high pressure pump, on MOJO I tee'd into my air conditioner pump. It's a centrifugal Little Giant magnetically coupled pump rated at 20 gpm. It's mounted below the waterline so it's continuously flooded. It can feed all 3 air conditioners and the watermaker simultaneously, or just feed the watermaker alone. I do not have a bypass loop on it. It has been working great for years. I think the fact that it's a centrifugal pump is the key.
mvmojo is offline   Reply With Quote
Old 20-06-2018, 11:35   #11
Senior Cruiser
 
Captain Bill's Avatar

Cruisers Forum Supporter

Join Date: Apr 2008
Location: Punta Gorda, Fl
Boat: Endeavourcat Sailcat 44
Posts: 2,711
Re: Water Maker low pressure supply pump

I have a variable speed pump on my fresh water water system, but the pressure is not adjustable, or at least I don't know how to adjust it. Do use a standard variable speed pump like the Jabsco VFLO or do you have a special sku with a lower operating pressure? That's a very good idea if you're going to use a 12v boost pump.
Captain Bill is offline   Reply With Quote
Old 20-06-2018, 21:23   #12
Registered User

Join Date: Apr 2007
Location: Australia
Boat: Island Packet 40
Posts: 2,842
Images: 7
Re: Water Maker low pressure supply pump

If you want to bypass some of the discharge water back to the pump suction you can place a check valve in the bypass to act as a very simple constant pressure relief valve. You need a poppet type valve with a spring not a flapper type valve. When the pump discharge pressure increases to the cracking pressure of the poppet it will open and then hold the pressure drop across the valve constant.

I used one on the cooling system on my last boat so that the impeller pump did not dead head against a closed thermostat and a high flow of cooling water would be maintained through the water cooled exhaust manifold and exhaust discharge hose.
RaymondR is online now   Reply With Quote
Old 20-06-2018, 21:25   #13
Marine Service Provider
 
SV THIRD DAY's Avatar

Community Sponsor
Cruisers Forum Supporter

Join Date: Aug 2006
Location: La Paz, Mexico
Boat: 1978 Hudson Force 50 Ketch
Posts: 3,804
Re: Water Maker low pressure supply pump

Quote:
Originally Posted by RaymondR View Post
If you want to bypass some of the discharge water back to the pump suction you can place a check valve in the bypass to act as a very simple constant pressure relief valve. .
Bingo....been doing that for years....it ain't rocket science folks.
__________________
Rich Boren owner of:
Cruise RO Water High Output Water Makers
Technautic CoolBlue Refrigeration
La Paz Cruisers Supply and Yacht Management and Brokerage
SV THIRD DAY is offline   Reply With Quote
Old 20-06-2018, 22:37   #14
Marine Service Provider

Join Date: Aug 2015
Location: Melbourne
Boat: Jenneau Prestige 46
Posts: 25
Send a message via Skype™ to desdestiny
Re: Water Maker low pressure supply pump

A comment on the subject of bypass water.
This will reduce the flow delivered to the RO watermaker.
However the pump motor will continue to run at full speed, AND will continue to run at highest temperature.
These motors do not have a fan and are not designed for 100% duty cycle.
The problem the person has with the motor cutting out after 40 minutes is because the thermal cutout triggered to stop the motor overheating.

These instruction manual for these pumps recommend they run for short time only - not continuous.
desdestiny is offline   Reply With Quote
Old 21-06-2018, 06:59   #15
Marine Service Provider
 
SV THIRD DAY's Avatar

Community Sponsor
Cruisers Forum Supporter

Join Date: Aug 2006
Location: La Paz, Mexico
Boat: 1978 Hudson Force 50 Ketch
Posts: 3,804
Re: Water Maker low pressure supply pump

Quote:
Originally Posted by desdestiny View Post
This will reduce the flow delivered to the RO watermaker.
However the pump motor will continue to run at full speed, AND will continue to run at highest temperature..
Not true.
The Amps used (and heat created) by the pump increases with additional pressure the pump is asked to create. So adding a bypass to a positive displacement diaphragm pump loweres the pressure of the pump and reduces the amps usage and heat. I know this from real life bench testing on our shop units that run continusouly 24hr/day....7 days/week.
SV THIRD DAY is offline   Reply With Quote
Reply

Tags
water

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
negative power supply and 12v negative battery supply same thing? er9 Marine Electronics 8 02-03-2016 08:06
Engine Rpm For Water Maker HP Water Pump Burge Construction, Maintenance & Refit 3 21-11-2015 09:42
Spectra Low Pressure Pump noelex 77 Plumbing Systems and Fixtures 6 08-11-2013 07:11
For Sale: Brand New Whale AP0816 Agri-Pump 12VDC Water Pressure Sprayer Pump v62cobra Classifieds Archive 0 15-12-2012 10:41
Low Oil Pressure at Low Revs Streetcar Engines and Propulsion Systems 6 16-03-2012 10:07



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 19:57.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2019, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.