On Board Water Pump

[SirRogerFFS]

Hi All, it was sometime ago I was having problems with the pump for my onboard water tank. Originally it was a flojet pump that decided to die on me . I wen to our dealer who only had a shurflo pump and me not thinking purchased this pump and I have had problems with air ever since Our good friend Sprocket pointed out some ideas that did improve my problem but only on the cold tap it knocks and bangs through the van on the hot side .This reallyis a beware post The Flojet pump was a 20 Psi Pump the replacement shurflo is 30 Psi and this is what seems the be the problem. So If any body has a flojet or shurflo 20Psi pump that is looking for a home . Im looking
Thanks every body that did originally join in on this topic

 

[ProfJohnL]

Hello Sir Roger,

Virtually all diaphragm pumps are capable of delivering surprisingly high water pressures usually well in excess of 30psi(2 Bar) what limits them is the pressure switch setting. Now I'm not sufficiently familiar now with all the recent pumps but the Shureflo models used to have a pressure switch adjustment screw which you could with judicious care tweek down to a more normal 15 to 20psi. have you been able to do this ?

 

[SirRogerFFS]

Hi Prof ..... Sadly John this shurflo is non adjustable It is something we had looked at in recent times.Its a strange thing that happens if you fully open the hot tap it doesnt create the knocking through the system. But when you part open the tap it does knock and runs on when you close the tap.I have got the pump running quietly when taps are open now but to go along with problem which I am fairly sure it is the pump when I drain the water down its has loads of air in before water runs .
Thanks for you input
Sir Roger

 

[Gafferbill]

........surely if air is in the system then you have a leak on the pipework between the pump and the water supply tank. Hard to detect as the leak will be air getting in rather than water getting out.

 

[SirRogerFFS]

Hi Gaffer Bill thanks for coming in on this one your thoughts are appreciated this problem came along only when the new shurflo pump was fitted again its a 30 psi pump as the flojet was 20 psi
Regards Sir Roger

 

[Gafferbill]

Exactly. ...so I would firstly be checking the inlet conections of the new pump to make sure they were not letting air in.

 

[SirRogerFFS]

Thanks again Gafferbill .I will take your point and will be in the van during the week as it is in storage at the moment.I s think I may still look for another pump as I feel that if the system is designed for a 20 psi pump then 30 may not be right either but as you say best go back to the beginning .
Thanks again Sir Roger .

 

[ProfJohnL]

Hi Prof ..... Sadly John this shurflo is non adjustable It is something we had looked at in recent times.Its a strange thing that happens if you fully open the hot tap it doesnt create the knocking through the system. But when you part open the tap it does knock and runs on when you close the tap.I have got the pump running quietly when taps are open now but to go along with problem which I am fairly sure it is the pump when I drain the water down its has loads of air in before water runs .
Thanks for you input
Sir Roger

The knocking description you have just added sound more like an airlock or air hammer somewhere in the system. It is just possible the essential air cap in the water heater and the length and size of the pipes and the power of the pump have just coincided to produce a resonant system. This could be brought on by running the system at a slightly higher pressure. This thought is supported by your report that when you fully open the system is quiet, but when only part open the flow resistance is enough to allow the pump to run up to trip pressure which starts the hammer.

I don't know which water heater you have, but all the Carver and Truma models were designed to have an air cap at the top to allow for the expansion of cold water as it was heated. This was achieved by having the water exit point a few cm below the top of the tank. After drain down the first refill needed to fill the tank and the entry of the cold water would displace the air in the tank until the water level reached the take off point. Obviously the hot taps needed to be open to allow the air to escape. The first few times some hot water was drawn off, it would often en train a little air from the air cap causing bubbles, but this would subside over the first 3 or 4 heating and take off cycles and is not usually a problem.

If some of that air has become trapped in a pipe that has not been properly vented, it may be reacting with pump pressure.

Check the priming instructions for you water heater, I hope you have tried opening ALL the taps and shower at the same time until you only get water and no air. Then closing them one at a time starting with the taps nearest to the pump.

There is nothing stopping you from fitting a whale type pressure switch just after the pump. These of course can be set at a lower pressure and might just cure the hunting problem.

What I cant explain is the amounts of air you have describe when draining down. Like Gaffer I do wonder if you have a leak somewhere on the system? Where I do deviate form gaffers thinking is generally with these diaphragm pumps the peak pressure they develop on every cycle would almost always cause a visible water leak. Do you have any water leaks anywhere, dripping taps, water heater vent valves, anything??

 

[SirRogerFFS]

Hi Prof I see you are a busy man solving mysteries at the moment.I will go back to the beginning when can go back to our van in storage. I shall start at the where the pipes join the pump But to answer you question there , there is not a leak at the pipes that joint to the pump. If there is getting in then as Gagfferbill pointed out as the pipes to the pump were the only ones disturbed so I will be checking this out carefully. I must repeat though the service engineer was concerned about the difference in pressures between the two pumps.I guess the 10 psi difference in that sort of system is a lot .
Regards Sr Roger

 

[Gafferbill]

.......don't forget that with an on board diaphragm water pump all the pipework between the pump and the water reservoir is subjected to a negative pressure (suction) and all the pipework from pump to the outlets is under a positive pressure.
So problems on the inlet side will manifest themselves as air entering the pipework.
(There could also be a smaller associated water leak when the pump is idle)

Problems on the outlet side will manifest as a relatively larger water leak.

 

[SirRogerFFS]

Gafferbill I am taking all you thoughts onboard.along with Sprocket.My intentions are when I go down to our van I will start from the beginning and silicone grease all the the joints I have put in.which is nrv each side of the onboard pump.+1nrv just inside the van after the whale pump. Now I have to say that nrv this sideof the whale pump did leak somewhat so the pipe that was leaking was replaced but it wasnt replaced with blue hose so I am now wondering if this pipework I replaced could be the culprit..Bill what are your thoughts of the this new pump being 10psi higher than the original pump as the engineer suggested this could have a bearing on the problem .Thanks for your input it has made me think where I check next . Regard Sir Roger

 

[ProfJohnL]

.......don't forget that with an on board diaphragm water pump all the pipework between the pump and the water reservoir is subjected to a negative pressure (suction) and all the pipework from pump to the outlets is under a positive pressure.
So problems on the inlet side will manifest themselves as air entering the pipework.
(There could also be a smaller associated water leak when the pump is idle)

Problems on the outlet side will manifest as a relatively larger water leak.

Good thinking Gaffer, I had forgotten to consider the suction side, and yes a leak near the inlet would draw air into the system, but also allow the standing water in the inlet to drain back to tank each time the pump stops.

The new pump will have an some effect on the suction side but exactly what that difference would be is not clear, the amount of suction you can achieve is limited by the ambient air pressure which of course is broadly the same for both pumps.

If you do have a leak as Gaffer has described, that wold explain the air in the pipes, and it would also set up the conditions for the water hammer effect. IF you find a leak and manage to clear it you may find the new pump works fine. BUT, back in the 1980's when I was more directly involved with caravans, the maximum cold water pressure was not meant to exceed 20psi, otherwise you may be in danger of blowing pipework joints and the water heater tanks ) 20psi on the cross sectional area of a typical hot water tank would produce over 1000 lbs thrust, and 30psa 1500lbs!

I still think it wold be wise to consider a standard pressure switch to control you new pump.

 

[Dustydog]

Sir Roger

Finally got wifi today!
Does the problem arise when using the water source from both the the onboard tank and or the aquaroll?

 

[SirRogerFFS]

Hi Dusty .Well ...Its only on the onboard water pump side and as I have said ,if you fully open the hot tap the problem is hardly noticeable .. Just to clarify trying different things when I drained down the water heater loads of air in it.. .there are a few things I think I need to do but as you are a practical man I wait your suggestions and thanks for joining in.
Sir Roger. PS Well done with the WIFI very handy to have .

 

[SirRogerFFS]

FAO Prof John Gafferbill and Dusty and Sprocket. Here is my plan.When I fitted the new pump I had to modify the pipework to the onboard Pump nothing serious easy to get at .Because of air issue I have put a none return valve each side of the onboard pump,it did improve slightly on the cold side . then tracking everything back I found a none return valve inside the van just after the Whale pump leaking.Now ...... I didnt want to use the pipe again that was leaking so I bought a new piece of pipe from our dealer now this maybe where my problem might be.The replacement pipe is not the Blue Pipe its coloured like a stick of rock. I am now wondering if this pipe is smaller albeit slightly enough to give me this problem Now when I go back to our van in storage I am going to go through all the pipes i have disturbed and put some silicone grease on each of the none return valves I have put in. Now my question is will putting silicone grease on the do any harm. Thank you everybody for the input
Sir Roger

 

[ProfJohnL]

Silicone grease won't harm the pipe or fittings but its not a good idea to have it near potable water or water that might be drunk if not by you , by who ever might have the caravan after you.

I can't recall teh name of teh product but there used to be a lubricant just for the potable plastic pipe fittings. I'd guess a plumbers merchant or serious DIY store may have the proper stuff.

Vegetable oil could be an alternative.

 

[Anseo]

Silicone grease won't harm the pipe or fittings but its not a good idea to have it near potable water or water that might be drunk if not by you , by who ever might have the caravan after you.

I can't recall teh name of teh product but there used to be a lubricant just for the potable plastic pipe fittings. I'd guess a plumbers merchant or serious DIY store may have the proper stuff.

Vegetable oil could be an alternative.

For O-rings and rubber seals in brake systems etc. I use red-rubber grease, a vegetable derivative it is claimed.

Not sure how health safe it is in potable water systems, but I am inclined to use it in preference to silicone based greases.

 

[SirRogerFFS]

Thanks Sir Haggis I have plenty to go at now .I shall be in the van most of Thursday if the weather permits .
Sir Roger

 

[Anseo]

Thanks Sir Haggis I have plenty to go at now .I shall be in the van most of Thursday if the weather permits .
Sir Roger

If you want some red rubber grease I can send you some, not sure how you share an email privately , I guess the mods would help. No charge my friend.

Regards,
Anseo.

 

[SirRogerFFS]

Anseo Many thanks for your offer but am sorted .Thank you all the same .
Regards Sir Roger

 

[otherclive]

I have a Flojet pump on the caravan and whilst it works okay I cannot for the life of me understand why Swift decided to locate it at the front of the caravan right under the double bed. Apart from the fact that it is near the water inlet and hot tank. Anyone using water at night cannot help but start the pump and what a racket it kicks up. So I now carry a 5 litre bottle of water for hand washing at night. Much prefer the external radial pumps.

 

[SirRogerFFS]

Other Clive .. I know what you mean .Our Flojet pump was situated under the front double bed and I must say mine was reasonable quiet but now with this Shurflo my Daughter is not happy about somebody
banging around in the van when you open the hot tap.Hopefully I will get it sorted tomorrow. If the work I am going to do doesnt cure it then I have to get a lower pressure pump. I dont mind I just want to stop the knocking .Its that bad people look round when you open the hot tap
Regards Sir Roger.

 

[SirRogerFFS]

Thank you everybody that contributed to this onboard water pump problem. This is where I am today I did as Gafferbill suggested and I have been back to every joint I made to facilitate this shurflo pump and refitted them. Now I have to say that when I tried the pump it made some strange noises but I have to say it does seem at this point quieter .Not being 100% happy I went back to a combination of joints at the bulkhead of the van where I found a nice non return valve that looks as though it maybe going back to the aquaroll on removal I found it wasnt closing fully so I have now replaced it with a new one .Sadly I cannot get hot water on storage site . I know I could have used gas but I couldnt mess about ..As it stands now it doesnt seem to be banging through the van as much its more of a rattle now . Can somebody please tell should this pump stop dead when you close the tap or does it run on for a few seconds
Thanks again .....Regards Sir Roger

 

[chrisn7]

The pump will run on briefly to restore the water pressure, whether the onboard or submersible in the Aquaroll.

 

[Gafferbill]

.....I am sure you will sort it Sir Roger.
We can only make suggestions over the internet.
I don't know if the higher output pump will cause any problems on your particular van......I would not have thought so providing pipe joints are secure.