cooling water back pressure - SailNet Community
 1Likes
  • 1 Post By colemj
 
LinkBack Thread Tools
post #1 of 3 Old 03-21-2020 Thread Starter
Master Mariner
 
capta's Avatar
 
Join Date: Jun 2011
Location: somewhere south of civilization
Posts: 8,097
Thanks: 179
Thanked 421 Times in 409 Posts
Rep Power: 9
 
cooling water back pressure

Sorry, not cooling water, but feed water.
We've been using a 12 volt Water Puppy (6.3 gpm) as a boost pump for our watermaker, but they do not like the back pressure from the high pressure pump (2.3 gpm) and over heat and fail after some time.
We have a 110 volt Dometic/March water cooled continuous duty magnetic drive pump (8.3 gpm) that will do the job quite nicely, but I have no idea if the back pressure will damage the magnetic drive pump.

I assume that the magnetic drive will not be affected by back pressure, as the Water Puppy was, because there is no direct drive between the motor and impeller. We have run the magnetic drive pump with the thru hull partially open and that does significantly reduce the water flow, but again, I have no idea if this will damage the pump.
We would appreciate any thoughts on this.

"Any idiot can make a boat go; it takes a sailor to stop one." Spike Africa aboard the schooner Wanderer in Sausalito, Ca. 1964.
“Believe me, my young friend, there is nothing - absolutely nothing - half so much worth doing as simply messing about in boats.” ― Kenneth Grahame, The Wind in the Willows

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

facebook.com/svskippingstone

Last edited by capta; 03-21-2020 at 04:59 PM.
capta is online now  
Sponsored Links
Advertisement
 
post #2 of 3 Old 03-21-2020
Senior Member
 
colemj's Avatar
 
Join Date: Jul 2003
Location: On the boat cruising
Posts: 3,559
Thanks: 5
Thanked 148 Times in 140 Posts
Rep Power: 17
 
Re: cooling water back pressure

I'm assuming you do not have a Spectra or similar energy recovery unit that uses the feed pump as a pressure pump.

If this is correct, then a March pump or similar magnetic drive will work just fine, as long as it is sized to provide sufficient flow to feed the HP pump. Don't go by its open flow rating, but look at where it is rated for ~3-4' head because this is more indicative of how it will be used in this application. We used one for several years on our previous boat.

Another option is to use a bypass valve on a diaphragm pump like the Water Puppy, that diverts extra flow beyond what the HP pump takes back into the feed stream. A bit difficult to explain, but you put the bypass valve in parallel between the input and output of the feed pump. The HP pump takes what it needs, and the remainder is just continually circulated. This way the feed pump does not turn on/off/on/off... and burn out - it just runs. Of course, it needs to be rated for continuous duty for this. We have also used this in a watermaker application for several years.

A third option is to use a variable speed pump like the Jabsco VFlow 5.0, which will run at high duty cycle, and adjust its flow to match that of the HP pump. Our current watermaker uses this pump, but it is new and I can't report on its long-term performance (although it is warranted by the watermaker company for 5yrs in this use).

Mark
capta likes this.

Dolphin 460 Catamaran "Reach"

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
- Current boat

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
- Previous boat
colemj is offline  
The Following User Says Thank You to colemj For This Useful Post:
capta (03-21-2020)
post #3 of 3 Old 03-21-2020 Thread Starter
Master Mariner
 
capta's Avatar
 
Join Date: Jun 2011
Location: somewhere south of civilization
Posts: 8,097
Thanks: 179
Thanked 421 Times in 409 Posts
Rep Power: 9
 
Re: cooling water back pressure

Thanks.
We are in full quarantine here so we've literally got to work with what we have aboard, so it's just the March pump and some hose. Your first answer pretty much confirms my assumption, so we'll have to go with that.
If and when I can acquire 3/4" hose barbs and hoses we'll replace the 1/2" lines which I hope will further alleviate the pressure to the high pressure pump, but who knows when that will be.

"Any idiot can make a boat go; it takes a sailor to stop one." Spike Africa aboard the schooner Wanderer in Sausalito, Ca. 1964.
“Believe me, my young friend, there is nothing - absolutely nothing - half so much worth doing as simply messing about in boats.” ― Kenneth Grahame, The Wind in the Willows

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

facebook.com/svskippingstone
capta is online now  
Reply

Quick Reply
Message:
Options

By choosing to post the reply above you agree to the rules you agreed to when joining Sailnet.
Click Here to view those rules.

Register Now



In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.


User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Posting Rules  
You may post new threads
You may 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 On
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome