Water Pumps

[floatsyourboat]

I am a bit confused how the water pump is supposed to work.

Is it switched on manually then you run the taps ect then switch the pump off or is there another way things can be done?

[Paul C]

THe "normal" way it works on a boat is the water pump is permantently connected to electricity, and there's 2 switches: the low pressure switch senses when the pressure falls below say 10psi and turns it on, the high pressure switches senses eg 25psi and turns it off. There's 2 pressures because if there was one pressure, the pump would be on and off much more frequently. When you open a tap there is nothing for the pump to 'push against' which gives rise to a force, thus a pressure, so the pressure drops and the pump starts. Then when the tap closes there is something (the closed valve in the tap) to push against, so the pressure rises.

 

Then there's an accumulator, which stores pressure and reduces the pump operation. In this case, there's a reservoir of pressurised water which doesn't just fall away when a tap is opened, instead the pressure in maintained in the water but the water within it is depleted, so its possible for the store of water to be eg 25psi then a tap opened for hand washing, and the store of (a bit less) water is now at say 15psi so the pump doesn't operate. When the tap is opened for another hand washing, the pressure drops eventually to below 10psi and the pump operates to bring it up to 25psi again. Instead of it being a quick process, the accumulator stores water as the pressure gradually rises.

 

The figures of pressure and time are approximate, but give the idea of what occurs.

[floatsyourboat]

Thanks for that.

So on an older sure flow pump would I need to add a relay or something for this process to happen or is it built into the pump?

[Paul C]

Do you have a model number, there's loads of variations of "older sure flow pump" out there!

[JDR]

On the Shurflo pumps I have seen the pressure switch mechanism is on the "top" of the pump where the connections are for the incoming and outgoing water connections, secured by four screws with an additional screw hidden by a label that can alledgedly be used to adjust cut in and cut out pressures. It is part of the pump, as long as it is connected correctly to a 12v supply no extra relays are required. I would advise leaving it alone if it is working OK as from memory when I took one apart there is a spring behind the switch and it can be a bit of a faff to put back together properly.

 

There are differing opinions on Shurflo pumps, I had one which was machine gun noisy but worked OK for years but the replacement was dead in 18 months. If you do need to replace the pressure switch there is also the option of buying an external inline pressure switch rather than using the one provided with pump. Whale used to sell them for around £20.

Edited August 3, 2014 by JDR

[LEO]

Hi,

 

I recently had problems with a Shurflo pump leaking -- I changed to a Jabsco - similar performance, size and price but with 'easy fit' connections and I was able to free up space by not using an accumulator..........

 

Search the posts - recent one - Shurflo pump - one memebr suggested a Whale water pump which slotted into the Shurflo/Jabsco range.

 

L