I saw relatively recent thread concerning problems with the water pump. Also looking at other Forums there seemed to be quite a lot of misinformation and confusion concerning location of NR Valves and their operation. I had my own issues and decided to have a crack at fixing it. These valve adjustments (located at the front of the pump) fix the following issues:
Backflow (Bypass) valve:
Mains water filling tanks
Air in water system (spitting taps)
Pump constantly running
Pumps appearing to operate in reverse (pumping to tanks)
Negative Head (pressure switch) valve:
Pump constantly running
Pump running on and off
Pump oscillating rather than running somoothly
Pump not running
Shower running hot and cold
Warning: I am not a plumber and have come with this information 'half-baked' in order that somebody will add to further information to make this more complete/useful/accurate.
I took off the pump and had a look a it's gizzards but this is not necessary. The only thing I found/confirmed by doing this is that the factory has no concept of correctly torquing fixings. Any screw torqued correctly is purely by accident. The only thing you need to rectify pump issues is a 2mm allen key (assuming the pump is ok). Make sure you have it (2mm hex) in your spares bag before attempting this or a road trip.
The theory - back-flow (bypass) valve
The primary issue (I think) is the setting of the back flow valve (which is part of the pump). This valve takes excessive pressure from the pump (outlet) and diverts it to the inlet (to be re-pumped/think 'wastegate'). I am guessing here but I think this is so that 2x taps (hot/cold) can be run at once and both hold good pressure... so the pump cfm exceeds the flow from one tap. The problem is therefore if the pressure from the mains connection exceeds the pressure setting (and the setting of the negative head pressure) then (mains) water will flow back into the tank.
Also if this valve is set below the pressure value of negative head valve (the next 'in-line') the pump will always be on and merely be circulating water (or air) through itself.
The Theory - negative head (pressure) valve
The negative head valve tells the pump when to turn on. Once the appropriate pressure is reached it turns the pump off. When you turn a (say kitchen) tap on the pressure in the system drops (ahead of the valve) and the pump activates to boost the pressure.
The theory - interaction b/w the negative head and back-flow valves
Without getting too far out of my sphere of limited knowledge/experience (I haven't quite worked out how to calibrate the system from scratch) I can confirm they need to be adjusted wrt each other. If either of these are set incorrectly then you will get problems although I suggest most people will need to adjust the backflow valve.
The theory - Other NRV protection
On my 2016 20' expanda I see no other NRV's (non-return valve) other than contained in the pump assembly. The backflow (bypass) valve noted above should function as an NRV if adjusted correctly.
The adjustment (with 2mm hex/allen key)
The Shurflow manual dictates how to fix the problem/calibrate the system with a pressure meter which I don't have. My problem was with the tank filling and air (recirculating via the back-flow valve) in the system. This happened only occasionally when mains pressure exceeded the back-flow valve setting. I would start out by adjusting the back-flow valve clockwise (increasing the pressure setting) so the valve remains shut when the system is under mains pressure (this also increases the pressure the pump will return/divert some excess pressure from the outlet to the inlet and the pump will be more likely to temporarily stop/be intermittent). I would adjust half a turn (clockwise) and turn on tap (for a few seconds) and leave it for a while to see if the tanks fill and if so keep doing half a turn. (keep a record of how far you adjust otherwise you won't know where you are). This may lead to the pump starting and stopping because the back-flow valve is not recirculating excess pressure. Also may lead to hot/cold water cycling (shower getting hot and cold).
Negative head/Pressure switch adjustment. I wouldn't touch this in the first instance however.... Turning clockwise will result in a more sensitive switch (more likely to cycle). Turning counterclockwise makes the pump less likely to cycle.
I attach a photo of the pump and the adjustment (2mm hex) grub screws (directly below centre of text). Also the pdf of the manual with more info.
Again I am 'half-baked' with this information and have so far cured my (backflow/spitting) problem but need more adjustment to get the pump return (bypass) operating correctly with the pressure switch/valve. I would not make too many adjustments without keeping a record of them and their impact on your system. Make small adjustments over sufficient time (a day or so) to fully determine their impact.
Backflow (Bypass) valve:
Mains water filling tanks
Air in water system (spitting taps)
Pump constantly running
Pumps appearing to operate in reverse (pumping to tanks)
Negative Head (pressure switch) valve:
Pump constantly running
Pump running on and off
Pump oscillating rather than running somoothly
Pump not running
Shower running hot and cold
Warning: I am not a plumber and have come with this information 'half-baked' in order that somebody will add to further information to make this more complete/useful/accurate.
I took off the pump and had a look a it's gizzards but this is not necessary. The only thing I found/confirmed by doing this is that the factory has no concept of correctly torquing fixings. Any screw torqued correctly is purely by accident. The only thing you need to rectify pump issues is a 2mm allen key (assuming the pump is ok). Make sure you have it (2mm hex) in your spares bag before attempting this or a road trip.
The theory - back-flow (bypass) valve
The primary issue (I think) is the setting of the back flow valve (which is part of the pump). This valve takes excessive pressure from the pump (outlet) and diverts it to the inlet (to be re-pumped/think 'wastegate'). I am guessing here but I think this is so that 2x taps (hot/cold) can be run at once and both hold good pressure... so the pump cfm exceeds the flow from one tap. The problem is therefore if the pressure from the mains connection exceeds the pressure setting (and the setting of the negative head pressure) then (mains) water will flow back into the tank.
Also if this valve is set below the pressure value of negative head valve (the next 'in-line') the pump will always be on and merely be circulating water (or air) through itself.
The Theory - negative head (pressure) valve
The negative head valve tells the pump when to turn on. Once the appropriate pressure is reached it turns the pump off. When you turn a (say kitchen) tap on the pressure in the system drops (ahead of the valve) and the pump activates to boost the pressure.
The theory - interaction b/w the negative head and back-flow valves
Without getting too far out of my sphere of limited knowledge/experience (I haven't quite worked out how to calibrate the system from scratch) I can confirm they need to be adjusted wrt each other. If either of these are set incorrectly then you will get problems although I suggest most people will need to adjust the backflow valve.
The theory - Other NRV protection
On my 2016 20' expanda I see no other NRV's (non-return valve) other than contained in the pump assembly. The backflow (bypass) valve noted above should function as an NRV if adjusted correctly.
The adjustment (with 2mm hex/allen key)
The Shurflow manual dictates how to fix the problem/calibrate the system with a pressure meter which I don't have. My problem was with the tank filling and air (recirculating via the back-flow valve) in the system. This happened only occasionally when mains pressure exceeded the back-flow valve setting. I would start out by adjusting the back-flow valve clockwise (increasing the pressure setting) so the valve remains shut when the system is under mains pressure (this also increases the pressure the pump will return/divert some excess pressure from the outlet to the inlet and the pump will be more likely to temporarily stop/be intermittent). I would adjust half a turn (clockwise) and turn on tap (for a few seconds) and leave it for a while to see if the tanks fill and if so keep doing half a turn. (keep a record of how far you adjust otherwise you won't know where you are). This may lead to the pump starting and stopping because the back-flow valve is not recirculating excess pressure. Also may lead to hot/cold water cycling (shower getting hot and cold).
Negative head/Pressure switch adjustment. I wouldn't touch this in the first instance however.... Turning clockwise will result in a more sensitive switch (more likely to cycle). Turning counterclockwise makes the pump less likely to cycle.
I attach a photo of the pump and the adjustment (2mm hex) grub screws (directly below centre of text). Also the pdf of the manual with more info.
Again I am 'half-baked' with this information and have so far cured my (backflow/spitting) problem but need more adjustment to get the pump return (bypass) operating correctly with the pressure switch/valve. I would not make too many adjustments without keeping a record of them and their impact on your system. Make small adjustments over sufficient time (a day or so) to fully determine their impact.
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