How pumps in fresh water system work

[earthmover17]

I have 2 shurflo fresh water pumps on my boat. I was wondering how these work. Specifically does one pump run at demand and then the other kicks on for volume? Do they cut in and out at different pressures. Or are they both supposed to run at the same time. I also don't know how the pressure switch works. Is it internal in the pump itself?
I just don't seem to get the water flow I think I should so I thought I'd start at the source.

Jack

 

[Gimme Time]

Probably need to pull the pump strainers off to clean off any debris collected in the screen. Cleaned mine last weekend for the first time and got quite a bit of off white plastic material from when the tank was originally installed. When they (SR) drilled the holes for the various lines in and out the plastic shavings from the drilling process were left in the tank. Once the water circulates around enough eventually some debris will flow to the pump head strainers.

As to how they operate, I have two pumps of which 95% of the time only one breaker is on so I limit the use to normally only one. If your breaker is on the pressure switch will cycle the pump on and off on demand. I normally on turn the second pump breaker on when I have guest in the front cabin or there will be a lot of water demand from multiple water flows being called for.

I also just replaced one of the pumps and put in a 2 GPM 30 PSI on breaker #1 while breaker #2 is a 3 GPM 55PSI pump. This allows me to lower the water pressure and flow as others aren't as water Conservative as I am. My own little way of stretching the water out while away from the docks.

Hope this helps.

 

[earthmover17]

Probably need to pull the pump strainers off to clean off any debris collected in the screen. Cleaned mine last weekend for the first time and got quite a bit of off white plastic material from when the tank was originally installed. When they (SR) drilled the holes for the various lines in and out the plastic shavings from the drilling process were left in the tank. Once the water circulates around enough eventually some debris will flow to the pump head strainers.

As to how they operate, I have two pumps of which 95% of the time only one breaker is on so I limit the use to normally only one. If your breaker is on the pressure switch will cycle the pump on and off on demand. I normally on turn the second pump breaker on when I have guest in the front cabin or there will be a lot of water demand from multiple water flows being called for.

I also just replaced one of the pumps and put in a 2 GPM 30 PSI on breaker #1 while breaker #2 is a 3 GPM 55PSI pump. This allows me to lower the water pressure and flow as others aren't as water Conservative as I am. My own little way of stretching the water out while away from the docks.

Hope this helps.

John,
That explains what I was in a quandry about. I thought as long as both switches were on both pumps would start when their pressure switches were activated. One of my pumps runs intermittently so I will probably just replace it.

Thanks Jack

 

[The Bill Collector]

"I also just replaced one of the pumps and put in a 2 GPM 30 PSI on breaker #1 while breaker #2 is a 3 GPM 55PSI pump. This allows me to lower the water pressure and flow as others aren't as water Conservative as I am. My own little way of stretching the water out while away from the docks."

I like this idea !! Good job :thumbsup:

 

[Gimme Time]

Mark, Some people would think you cut your water conservation by a 1/3. But the way I look at it I'm keeping water wasters from using 50% more water than they probably need. Good luck as I like the 2 different flow & pressure options we have which allow us to help control someone's waste fullness.

 

[Dave S]

One of my pumps runs intermittently so I will probably just replace it.

I just replaced my Shurflo pump because it would not turn off. Afterwards I took the old one apart to see what might be wrong. One of the things I found out is the sensitivity of the presure switch itself can be adjusted very easily. If you look at the pump end you will see a screw in the center of the switch. You turn that screw to increase or decrease sensitivity and cycling. You may want to give that a try first. From what I know, turning the screw in (clockwise) would require a higher pressure build up to turn the pump off while turning the screw counter clockwise would require less pressure to turn the switch off and may also cause cycling. So I would first try turning that screw in maybe a quarter of a turn and see what happens.

Shurflo's web site has downloads for each pump and they talk a little bit about this adjustment in one of those downloads. It may be of some help but I found taking my apart helped me to understand how this thing works. Sadly that is probably all I needed to do to mine to "fix" it. Here is the link to their site http://legacy.shurflo.com/pages/Marine/marine_categories/potable/potable2.html

If you do decide to get another one, the best price on these things can be found at B O A T F I X

Dave

 

[earthmover17]

Dave,
Thanks for the heads up. I think I will try to adjust the pressure screw before I spend the money.

Jack

 

[Jackie J V]

Great thread - relevant to me.

I was wondering the same thing as Earthmover. One of my pumps was constantly cycling (pump #1) so I left it off - other things to contend with. By the time I got back to investigating - it was working fine. The only thing I changed plumbing wise, was to change out a cartridge in the Master shower (faulty and wasn't getting hot water).

If the problem kicks up again in the spring - I'll look at adjusting the screw as recommended.

I also do not seem to be getting the water pressure I think I should, especially on the port side systems (for whatever reason). How do I remove the pump strainers as recommended by Gimme Time? Is it relatively self-evident when looking at the pump?