Poor water flow from pump

[hymerholidays]

Hi again. Second problem to fix now is with the pump in the fresh water tank. It’s supposed to deliver 19 litres per minute but it’s not delivering anything like that. Very poor flow. Now, this is a new pump, that is new old stock, given to me by another Motorhome owner who no longer had his Hymer. Could it just be a case of age corrosion, even though it was new and unused in the box? Is there anything else I can try or do I just need to buy another pump? Sorry for all the questions but I’m trying to sort out all the systems in the camper and I’m not at all mechanically minded!

 

[Diabalo]

Have you checked that you have 12v to the pump?

 

[Lenny HB]

Try reversing the connections to the pump, although Hymer electrics are blue positive, brown negative those pumps are the other way round.
Also the pump has two motors one could have failed

 

[hymerholidays]

Have you checked that you have 12v to the pump?

Yes, it is running just not much water coming out.

 

[hymerholidays]

Try reversing the connections to the pump, although Hymer electrics are blue positive, brown negative those pumps are the other way round.
Also the pump has two motors one could have failed

The two motors thing sounds likely. Is the solution to buy a new pump?

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[Lenny HB]

The two motors thing sounds likely. Is the solution to buy a new pump?

If that's the problem, yes.
Try like I suggested swapping the connections first.

Another thought is the non return valve opening properly?

 

[Lenny HB]

The two motors thing sounds likely. Is the solution to buy a new pump?

If that's the problem, yes.
Try like I suggested swapping the connections first.

Another thought is the non return valve opening properly?

 

[hymerholidays]

If that's the problem, yes.
Try like I suggested swapping the connections first.

Another thought is the non return valve opening properly?

I’ll try swapping the connections first. The non return valve is working properly. Knowing my luck it’ll be new pump needed. Do I have to buy from Hymer? Or any other?

 

[Lenny HB]

I’ll try swapping the connections first. The non return valve is working properly. Knowing my luck it’ll be new pump needed. Do I have to buy from Hymer? Or any other?

It's just a standard Reich tandem pump, plenty on eBay & Amazon, make sure you get the correct one they come with & without the non return valve.

 

[ManTheVan]

I replaced our Shurflo which had developed a leak, with a new one of the exact same model. The new pump does seem to have a lower flow rate, but it’s sufficient. No idea why the difference.

One other consideration is that if the flow rate is actually do-able, it will result in you using water at a lower rate, meaning your reserves will likely last longer.

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[dabhand]

Also the pump has two motors one could have failed

Agree with Lenny, sounds most likely and if so the other will fail soon most likely

 

[Reallyretired]

I have the same pump and working OK at present. I always carry a spare as you're well stuck if the pump fails. Available from Amazon.

 

[Landy Andy]

If it’s a submersible pump, is it peeing water out the top, so only a limited amount is going up the pipe?

 

[dawsey]

19 litres per minute is absolutely huge. Almost power shower flow rates. Are you sure you want to empty your water tank with a single 5minute shower?

Motorhome submersible water pumps will typically deliver about 3.5-4 ltr/min out of the taps/shower heads. A 100-120 litre tank should last 30mins as a result.

All pumps of any type have a flow vs pressure profile (a pump curve). Maximum flow as may be printed on a label will always assume zero restriction/load/head/pressure ie the flow at an unrestricted pump outlet is quoted.

Add pipes, bends, non return valves, the flow delivered will start to drop.

Add longer pipes, a boiler, some height difference between tank and outlet (pressure head) and the flow drops further

Add then the restrictions of small pipes running to the tap and the tap itself and it drops even further.

Thus a submersible (usually vane type) pump with 19 lpm maximum flow printed on a label might actually deliver a max of approx 3-5 lpm (application dependent) out of your shower head once installed in the application.

It is normal, just a manufacturers design and specification compromise that is required due to a limited water supply.

 

[dabhand]

I’ll try swapping the connections first. The non return valve is working properly. Knowing my luck it’ll be new pump needed. Do I have to buy from Hymer? Or any other?

Whereabouts are you? Pretty sure I’ve got one in the garage

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[wfdTamar]

, make sure you get the correct one they come with & without the non return valve.

Which does a Hymer need?

 

[Lenny HB]

Which does a Hymer need?

Depends, our last Hymer was without current one was with, I say was as I got rid and fitted a Shureflo pressure pump.

 

[Figaro]

Which does a Hymer need?

It needs a NRV, sometimes they're a separate inline unit, or attached to the pump.

 

[dawsey]

For OP, have you actually measured your output flow using watch and a container of known volume?

Don’t want to teach anyone to suck eggs, but if unsure just measure the time it takes (in seconds) to fill a 1 litre container.

Then simply divide 60 by the time it takes (in seconds), and you get your delivery flow rate in litres per minute (ltr/min)

For example:

if it takes 15 seconds to fill the container, then 60/15 = 4 litres per minute. This would be normal, maybe a tad on the high side for a ‘normal’ camper van pump.

if it takes 45 seconds, then 60/45 = 1.3 ltr/min. This would be low.

The pipes, boiler, taps etc will be rated for far higher pressures than the typical camper van pump will be capable of delivering, leaving scope to fit high pressure/high flow pumps if desired. These can be a nice luxury for those who are perhaps less concerned about conserving water, for example always staying in places near a tap, and can refill the tank (always the limiting factor) every day. 8-9lpm is very high flow and would be the same as a decent shower in a house. For anyone that remembers (or maybe still has) those old ‘power showers’ with the noisy pumps, these things deliver around 20lpm, which as mentioned, isn’t really practical in a camper as the pressures required to force that volumetric flow rate of water through the little pipes of a camper van would almost certainly blow the boiler. (as well as emptying the tank in 5mins)

If you have very low flow, less than 2 lpm you might have a sticking non return valve, partly blocked inline filters or even some debris in the pipes from failed components, this happened to me and I sorted by disconnecting pipes from the boiler, (important) and back flushing using mains water pressure. I think my issue was a broken up auto purge (bleed) valve, which on inspection was not functioning. I never found the offending bits, it/they would have been fired somewhere into the bushes.

For us, a slightly dribbley shower is just part and parcel of camping and worth it to make the water last a little longer. When ours last failed I selected a pump to give 3.8 lpm flow at the taps. With our slightly bigger water tank (120l) we can eke out 34mins of run time from a full tank and just about have a decent-ish shower (‘decent-ish’ is defined by the Mrs’s or not on whether she is able to properly wash her hair.

She still always seems to use up more than half a bloody tank when doing so though….

 

[Bodoge]

Hi again. Second problem to fix now is with the pump in the fresh water tank. It’s supposed to deliver 19 litres per minute but it’s not delivering anything like that. Very poor flow. Now, this is a new pump, that is new old stock, given to me by another Motorhome owner who no longer had his Hymer. Could it just be a case of age corrosion, even though it was new and unused in the box? Is there anything else I can try or do I just need to buy another pump? Sorry for all the questions but I’m trying to sort out all the systems in the camper and I’m not at all mechanically minded!

To obtain a high output you need a high input, have you checked strainers and filters and pipes for obstructions, the pump can only deliver what it draws in. If that's all clear, check that the impellers are rotating, if they are then the pump isn't going fast enough to increase delivery pressure.

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[hymerholidays]

19 litres per minute is absolutely huge. Almost power shower flow rates. Are you sure you want to empty your water tank with a single 5minute shower?

Motorhome submersible water pumps will typically deliver about 3.5-4 ltr/min out of the taps/shower heads. A 100-120 litre tank should last 30mins as a result.

All pumps of any type have a flow vs pressure profile (a pump curve). Maximum flow as may be printed on a label will always assume zero restriction/load/head/pressure ie the flow at an unrestricted pump outlet is quoted.

Add pipes, bends, non return valves, the flow delivered will start to drop.

Add longer pipes, a boiler, some height difference between tank and outlet (pressure head) and the flow drops further

Add then the restrictions of small pipes running to the tap and the tap itself and it drops even further.

Thus a submersible (usually vane type) pump with 19 lpm maximum flow printed on a label might actually deliver a max of approx 3-5 lpm (application dependent) out of your shower head once installed in the application.

It is normal, just a manufacturers design and specification compromise that is required due to a limited water supply.

Thanks for the information. It sounded like an awful lot to me but I was just reading what was on the pump. I definitely don’t want to be wasting water so I’m pleased to hear that 3-5lpm is sufficient.

 

[hymerholidays]

For OP, have you actually measured your output flow using watch and a container of known volume?

Don’t want to teach anyone to suck eggs, but if unsure just measure the time it takes (in seconds) to fill a 1 litre container.

Then simply divide 60 by the time it takes (in seconds), and you get your delivery flow rate in litres per minute (ltr/min)

For example:

if it takes 15 seconds to fill the container, then 60/15 = 4 litres per minute. This would be normal, maybe a tad on the high side for a ‘normal’ camper van pump.

if it takes 45 seconds, then 60/45 = 1.3 ltr/min. This would be low.

The pipes, boiler, taps etc will be rated for far higher pressures than the typical camper van pump will be capable of delivering, leaving scope to fit high pressure/high flow pumps if desired. These can be a nice luxury for those who are perhaps less concerned about conserving water, for example always staying in places near a tap, and can refill the tank (always the limiting factor) every day. 8-9lpm is very high flow and would be the same as a decent shower in a house. For anyone that remembers (or maybe still has) those old ‘power showers’ with the noisy pumps, these things deliver around 20lpm, which as mentioned, isn’t really practical in a camper as the pressures required to force that volumetric flow rate of water through the little pipes of a camper van would almost certainly blow the boiler. (as well as emptying the tank in 5mins)

If you have very low flow, less than 2 lpm you might have a sticking non return valve, partly blocked inline filters or even some debris in the pipes from failed components, this happened to me and I sorted by disconnecting pipes from the boiler, (important) and back flushing using mains water pressure. I think my issue was a broken up auto purge (bleed) valve, which on inspection was not functioning. I never found the offending bits, it/they would have been fired somewhere into the bushes.

For us, a slightly dribbley shower is just part and parcel of camping and worth it to make the water last a little longer. When ours last failed I selected a pump to give 3.8 lpm flow at the taps. With our slightly bigger water tank (120l) we can eke out 34mins of run time from a full tank and just about have a decent-ish shower (‘decent-ish’ is defined by the Mrs’s or not on whether she is able to properly wash her hair.

She still always seems to use up more than half a bloody tank when doing so though….

Excellent advice and information. I’m new to all the technical stuff. I’m afraid I used to leave all that to my husband but he has become quite unwell so I need to step up.

 

[wfdTamar]

I have a reich twin which is 19 litres per minute and it is not ‘too much’ or wasteful (unless it’s only ever been running on one side of it). The other thing is that’s the maximum. You don’t have to have your tap fully open. I can get anything from a dribble to a good solid spray.

 

[dawsey]

I have a reich twin which is 19 litres per minute and it is not ‘too much’ or wasteful (unless it’s only ever been running on one side of it). The other thing is that’s the maximum. You don’t have to have your tap fully open. I can get anything from a dribble to a good solid spray.

Not a chance. Whatever number may be printed on the side of the pump, for the reasons I have previously explained you will not get anywhere near flow that from a camper van tap. Measure it to see for yourself, using the method I have also explained.

 

[wfdTamar]

19 is what it’s rated at I meant, but yes it’s nothing like that at the tap. More like about 4. It’s a good amount for a motorhome, but nothing like a good house tap. That’s why I wonder if one rated as low as 3-4 would be any good.

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[dawsey]

19 is what it’s rated at I meant, but yes it’s nothing like that at the tap. More like about 4. It’s a good amount for a motorhome, but nothing like a good house tap. That’s why I wonder if one rated as low as 3-4 would be any good.

It could be, it depends on the type of pump. A genuine high pressure pump (internal/external gear or for water most likely a diaphragm type) would deliver close to maximum flow at the tap. This are usually not recommended for a camper due to the potential to burst hoses and blow boilers (limit switch dependence), but with pressure switches they can be used, however if the pressure switch fails they will still blow the water jacket. Hence the typical use of impeller or vane pumps with steep pump curves with peak pressure of roughly a bar or 10m of ‘head’ if the pump is ‘deadheaded’. It protects the campers plumbing and most importantly the boiler. Very inefficient though, hence yes 3-4lpm typical out of the taps in a common camper application for a 19lpm ‘unloaded rated’ impeller pump.