Boost pump cycling.

[jakefouro]

Hi All,

I recently added a 3 bar twin booster pump to boost the pressure to all outlets on my vented domestic water system. Its working out very well except the pump cycles on and off after flushing the toilet and also when the dishwasher is filling. Thinking of adding two expansion/accumulator tanks to the hot and cold circuits. What size tank would I need and set at what pressure. Ta in advance.

 

[oldbuffer]

1. So the pump is doing what it is supposed to do. Open an outlet, (tap, WC dishwasher) and pump kicks in.
2. Why would you want to add expansion tanks? Its not going to do anything about the pump turning on and off.
3. Out of interest, what pump did you install?

 

[jakefouro]

Hi - ITs a Techflo T3 - I think Stewart Turner manufactured them. With the dishwasher the pump cycles on and off every 1 second or less which cant be good for the pump. Was thinking a 5l or 10l pressure tank on the cold circuit would stop this?

 

[Madrab]

Was thinking a 5l or 10l pressure tank on the cold circuit would stop this

Probably not, your issue is that the pump flow switches think that there is a call for water, an extra EV wouldn't stop the movement of water/change in pressure up to the pump switch.

Solenoid valves (on the DW) and float valves can be a trigger, as one can be twitchy when in use and the other can be either slow or sudden closing.

Is it a negative head pump, i.e. it has a mini EV on it?

 

[jakefouro]

Yeah its a positive head pump - its probably the solenoid in the dishwasher not allowing a strong flow of water past - pump reacts the same way if I open a tap partially - might have to connect the dishwasher directly to the attic expansion tank?

 

[Madrab]

Is your dishwasher not in the kitchen and running off the same mains as the kitchen sink cold supply should be?

 

[jakefouro]

Rob I have the dishwasher connected to a hot water supply utilizing the solar panels to reduce energy consumption. Have done so since panels installed 10 years ago without any issues. I can easily switch back to the cold supply if I have to though.

 

[Madrab]

Ah ok, good idea, saves the DW having to heat it. I take it the DW is rated to take a Hot Water fill supply?
Not all are and it can mess with the DW internal feeds (solenoid valve is part of that) and the programming.

 

[Madrab]

... I wouldn't connect it to the attic expansion tank, that's for the central heating. Or are you talking about connecting off the mains feed to it or are you talking about the large main cold water storage cistern (CWSC), if so it might struggle if the pressure isn't great.

 

[dilalio]

All sounds a bit Heath Robinson to me!
No kitchen appliances should be tank fed cold and only taps should be hot feed!

 

[jakefouro]

So at the moment I have the large CWSC in the attic with one outlet going to the hot water cylinder and the other directly to the booster pump. Central heating is an unvented setup. outlet from hot water cylinder goes directly to pump as well. Outlets from the pump feed two 6 port manifolds with supply the various outlets around the house. Kitchen sink cold supply is mains fed but pressure is low. Some booster pumps come with a small expansion vessel to reduce the pump cycling on and off if you just want to wash your hands. Its a single storey house and all pipework is in the attic.

 

[Madrab]

Some booster pumps come with a small expansion vessel to reduce the pump cycling on and off if you just want to wash your hands.

If you are talking about shower or whole house pumps that come with a small expansion vessel on top? They are universal or negative head pumps when there is little or no head of water. The pre-charged pressure in the vessel keeps the water in the pipe under that pressure, when you open the outlet the pressure is released and the water moves in the pipe triggering the flow switch and turning on the pump.

It has nothing to do with the pump cycling on and off if you want to wash your hands I'm afraid.

 

[jakefouro]

I think you gave answered my query Rob. I have the option of switching the dishwasher back to the mains supply. Thanks again.