Adjusting cut in pressure on a Shurflo pump

[pirate paul]

We have a Shurflo water pump like this one. Is it possible/advisable to raise the cut in pressure on the pump. We have a accumulator tank in the system, and it seems to work well in most respects. Open the tap and get a steady stream of water as the pressure in the accumulator is used up. The problem is that the pump waits until the stream has died away to a dribble before it cuts in and starts pumping. It's particularly annoying if you only have the tap open a bit as then the flow dies almost to nothing and you have to wait quite a while for the pump to kick in. Either that or you open the tap further and then get sprayed with water when it does suddenly kick in! It would be better if it cut in earlier, can I adjust this, and would there be any disadvantages to watch for? I don't need to change the high pressure cut out, just the low pressure cut in.

There is air in your pipes, the air is elastic, the delay is caused by the time taken for the air to expand, in my opinion, I do not have an accu tank but I go have the same pump.

[Iain_S]

(snip)

 

Where is this hole exactly? I know there's an adjustment screw on the head of the pump in the centre of the pressure switch. I think this adjusts cut in pressure, but it seems to make no difference to the problem.

 

It's internal. If you take the pressure switch off the pump , it's on the back of the switch. Be careful removing the switch; if it's like mine, it separates into its component parts, powered by the spring, as soon as you remove it. My pump isn't adjustable, so is a different model, but mine has four screws on the switch body, which attach to the pump.

 

Iain

[pirate paul]

It's internal. If you take the pressure switch off the pump , it's on the back of the switch. Be careful removing the switch; if it's like mine, it separates into its component parts, powered by the spring, as soon as you remove it. My pump isn't adjustable, so is a different model, but mine has four screws on the switch body, which attach to the pump.

 

Iain

You can get replacement switches, the do twang easy, I advise you do not take the switch apart.

 

I am sure the prob is air. There is an air lock, when the tap is turned off the pump stays on for a few moments, pressure builds up in the pipes, the air is compressed, when you open the tap the air can only decompress when some water has been removed from the circuit, the switch can not trigger until the diaphram is decompressed. This explains why it happens.

[blackrose]

I recently replaced my pump with the same model . I don't have an accumulator and since replacement the calorifier is dribbling. It's not a real problem , just annoying . I was wondering if it is easy to cure . I don't want the calorifier to blow when it heats up so I'm not keen to play with the release valve on it.

Is the pump adjustable ?

You're relying on the calorifier's pressure release valve to stop your calorifier from blowing and you're wasting a lot of hot water by just pouring it into the canal. If the PRV ever gets stuck and fails then it's goodnight Vienna! Some of that expansion will back up the cold pipe leading to the calorifier so I hope you DON'T have a non-return valve in that pipe.

I have a NRV in my setup so I installed a hot water expansion tank Td off between the NRV and the calorifier. It looks just like a large accumulator but it does a different job.

Edited September 6, 2009 by blackrose

[pirate paul]

You're relying on the calorifier's pressure release valve to stop your calorifier from blowing and you're wasting a lot of hot water by just pouring it into the canal. If the PRV ever gets stuck and fails then it's goodnight Vienna! Some of that expansion will back up the cold pipe leading to the calorifier so I hope you DON'T have a non-return valve in that pipe.

I have a NRV in my setup so I installed a hot water expansion tank Td off between the NRV and the calorifier. It looks just like a large accumulator but it does a different job.

Not the foggiest idea of what you are talking about, its air somewhere but where o where is the air.

[Trilby Tim]

Accumulator is set to 14 psi without any other pressure in the system. The pump is brand new, and has always worked like this, like for blackrose. The fault isn't really intermittent, but the exact pressure at which the pump kicks in does seem to change slightly, it's always too low though. This makes me think it's the factory settings on the pump which are a little out. I can't find any instructions on line or that came with the pump on how to adjust the cut in pressure, hence the question, I'll try phoning Shurflo next.

If anything I think having air in the system would help, after all that's the whole point of having an accumlator, a big reservoir of air that's compressed by the water pressure.

[RobinJ]

I have a Shurflo Aqua King (looks like the same model as Tim's) 20psi cut in - 30psi cut out. My accumulator is set to 17psi and I have a hot water expansion tank on my calorifier that's set to 33psi. (According to previous discussions on the forum these are the correct pressures). The pressure of both tanks was set with the pump switched off and taps open so there was no pressure in the system.

I have exactly the same problem with the water flow as Tim describes.

Most pumps are designed to operate at around 25 - 40 psi, on this one there should be an adjustment screw on the end of the pump which controls the pressure switch. There isn't normally a separate adjustment for cut in and cut out pressure.

If the pump developes about 30 psi when it swithes off, then you want to set up your accumulator for about 10 psi when the system is empty (pump isolated, taps open), this maximises your volume.

If the pump pressure is set correctly but it is taking a long time for the water pressure to drop before the pump kicks in again, it may be you have a restriction/blockage which is interfering with water flow?

[alan_fincher]

I'll try to remember to see what Shurflo documentation I have on the boat, when next there.

 

I have an older model, but clearly the principles are the same.

 

From memory, the only thing you can adjust was the point at which the pump cuts out, not the one at which it cuts in.

 

I'm sure my pump only has one adjustment, (it is a screw that's normally concealed by a label), but unless that affects both pressures, I don't think it will help with cut in.

 

But I could be wrong, so will see what I have.

 

I'm surprised the documentation is not readily available online TBH, but I can't quickly find any that relates.

[Trilby Tim]

From a bit more internet searching there seems to be one adjusting screw on the pump which adjusts both the cut out and cut in pressures. The pump's rated as a "30psi" model, but measuring the air pressure in the accumulator while the pump's pumping (which should be equal to the water pressure in the system) revealed that it was actually cutting out at 24 psi. I adjusted the screw on the pump so that it now cuts out at 29 psi, and it seems to have also raised the cut in pressure to a much more acceptable level, so we now get a pretty much even flow of water. Jobs a good 'un.

[WotEver]

I'm surprised the documentation is not readily available online TBH, but I can't quickly find any that relates.

 

Linky to manuals for all current shurflo products

 

T

[DHutch]

I have to admit, im very tempted to simply say "thats what they all do".

 

It is fairly well know that with a cut off of around 30psi and a cut in of around 20psi the shurflos dont maintain the most stable of pressures. Presumably they where set like this to allow at least semi-reasonable duty times when used without an accumulator. The pressure switch is also not the most complex or expensive.

 

Hence and option explored by several is having fitted an accumulator, to purchase a decent proprietary pressure switch with separately adjustable cutin and cutout pressures and use that inplace of the shurflos own switch.

 

 

Daniel

[Trilby Tim]

It's much better now, but I'm tempted by an external pressure switch with separately adjustable cut out and in pressures. Any suggestions of where I can get such an item? I've tried Googling, but can't find anything that's not meant for massive industrial applications!

Ta

 

I have to admit, im very tempted to simply say "thats what they all do".

 

It is fairly well know that with a cut off of around 30psi and a cut in of around 20psi the shurflos dont maintain the most stable of pressures. Presumably they where set like this to allow at least semi-reasonable duty times when used without an accumulator. The pressure switch is also not the most complex or expensive.

 

Hence and option explored by several is having fitted an accumulator, to purchase a decent proprietary pressure switch with separately adjustable cutin and cutout pressures and use that inplace of the shurflos own switch.

 

 

Daniel

[WotEver]

Any suggestions of where I can get such an item?

 

Here's one: http://www.marinescene.co.uk/product/1510/...pressure-switch

 

T

[Trilby Tim]

Thanks for the link, but according to the instruction sheet it doesn't have a separate cut in and cut out, just a combined one like the integral one already fitted.

 

Here's one: http://www.marinescene.co.uk/product/1510/...pressure-switch

 

T

[Keeping Up]

Thanks for the link, but according to the instruction sheet it doesn't have a separate cut in and cut out, just a combined one like the integral one already fitted.

The "Square D" is the most commonly used adjustable switch. They are very well made, and have independent adjustment of cut-in and cut-out pressure. They are available from most good chandleries.

 

Linky

 

Edited to correct link

Edited October 10, 2009 by Keeping Up

[David Schweizer]

It's much better now, but I'm tempted by an external pressure switch with separately adjustable cut out and in pressures. Any suggestions of where I can get such an item? I've tried Googling, but can't find anything that's not meant for massive industrial applications!

Ta

I would not bother unless you are in a very hard water area. I used to have one on my pump, and as an experiment, disconnected it and operated the shurflo pump with it's own pressure switch, there was no difference in performance.

 

The only exception would be if you are in a hard water area where the pumps integral switch can become clogged with lime scale causing rapid cut in and acut out cycles, and you cannot be bothered or are not confident enough to remove it and clean it out.

 

Despite warnings above, it is really quite east to remove and clean the pressure switch if you do it with the pump on the bench, all, you need is a small soft toothbrush to brush out the soft lime scale. and then re assemble the switch. If you are unlucky and the small diaphragm in the switch is damaged, you can buy a replacement from most decent Chandleries.

Edited October 10, 2009 by David Schweizer

[smileypete]

It's much better now, but I'm tempted by an external pressure switch with separately adjustable cut out and in pressures. Any suggestions of where I can get such an item? I've tried Googling, but can't find anything that's not meant for massive industrial applications!

Ta

I'd be tempted to put the money into a spare pump, for if (or rather when) the pump fails :lol:

 

cheers,

Pete.

[fastcarmiracledrug]

This was some advice given to me by chris w which I passed on to a couple who were having exactly the same problem as this.

 

Has you accumulator got a valve on it that resembles a tyre valve? (can't remember exact name of them)

 

If yes the bladder may need pumping up to the pressure shown above. (as mayalld has also mentioned)

 

The couple I mentioned used a foot pump with a pressure guage and it worked a treat.

 

It may be worth a quick check before adjusting / condemming the pump.

 

GB

HI WE HAVE AN ACCUMULATRTANK WITH VALVE FOR CAR PUMP AT TOP BUT WHEN I TRIED TO FIT PUMP WATER COMES OUT DOES THIS MEAN TANK IS KNACKERED?ALSO SHURFLO PUMP SEEMS TO LEAK VERY SMALL AMOUNTS AND DOESNT CUT OUT TILL FEW SECONDS OR LONGER AFTER TAPS HAVE BEEN SWITHED OFF WOULD APPRECIATE ANY INFO BEFORE REPLACING ANYTHING

[choogh]

HI WE HAVE AN ACCUMULATRTANK WITH VALVE FOR CAR PUMP AT TOP BUT WHEN I TRIED TO FIT PUMP WATER COMES OUT DOES THIS MEAN TANK IS KNACKERED?ALSO SHURFLO PUMP SEEMS TO LEAK VERY SMALL AMOUNTS AND DOESNT CUT OUT TILL FEW SECONDS OR LONGER AFTER TAPS HAVE BEEN SWITHED OFF WOULD APPRECIATE ANY INFO BEFORE REPLACING ANYTHING

 

Yes the diaphram/bladder is passing water. It need replacing. Never had these problems with the Godwin's.

[tone]

Fixed mine in 10 minutes, can i upload pictures?