Walrus HQ200 expansion vessel pressure

EmmWest

I have a Walrus HQ200 pump installed with an indirect unvented hot tank. The expansion vessel is 25L and is pressurised to 3 bar. I don't think this pump can exceed 3 bar. The pump cycles fairly often, pump anti-cycling bladder is at .85bar.

Can I drop the pressure in the 25L expansion vessel to improve this performance?

Thanks in advance

John.G

Yes, with pump off and pipe disconnected from its water end, reduce air end pressure to 1.5 bar.

Ideally the air end precharge pressure should be 0.2 bar lower than the pump cut in pressure or if mains fed, 0.2 bar lower than the PRV cold water setting.

EmmWest

https://www.boards.ie/discussion/comment/119662394#Comment_119662394

Thanks John,

That's roughly what I was thinking. I have set the expansion tank to 1.5bar air side with water end disconnected. I put all back together and turn on pump as normal. The pump still starts almost immediately when a tap is opened(even a small mount). The bladder on the pump is pressurised to 0.8 bar (pump off and water disconnected).

Do you know is there an adjustment on the pump itself at what pressure it cuts in?

John.G

Generally with a pumped unvented HW Cylinder one might expect the pressure switch to be on the cyl itself but your pump might be supplying the cold pressurised water as well either in single ended pump form or double ended pump, in which case the pump will have its own little pressute vessel?? Maybe reduce the 25L EV pressure to that of the 0pump bladder, ie o.85bar.

EmmWest

The pressure switch looks to be in the top of the pump, just nowhere obvious to change any settings. The pump supplies the tank through the prv, balanced cold then comes off the prv also (pic attached). I will try reducing the pressure in the 25L tank to 0.85bar so and see what happens.

25L vessel is the white one at the top-back. Red one is on the central heating.

John.G

HQ-EW.pdf

After adjustment, you can monitor the air end pressure at pump cut out & possibly at cut in. The HQ200 has a max head of 24M = 2.4bar, pressure vessel default setting is 0.8bar. If you reduce the cyl EV precharge to 0.8bar & assuming pump cut out at 2.4bar then the EV will expel 12L in falling to 0.8bar, if pump cut in is, for whatever reason at its max recommended cut in pressure of 1.6bar then the EV will only provide - 3L in falling to 1.6bar. Assuming a 250L cyl then the final pressure if whole contents heated to 60C will be 4.1bar after expansion but will fall to the pump pressure once a few litres of HW are drawn off.

EmmWest

Hi John,

Thanks for this information it was very helpful. I have tried a range of pressure settings and nothing seems to make much of a difference. I will probably change the pump in time.

Thanks again

John.G

Hi,

Just been thinking about that again, as set up originally, 25L EV at 3.0 bar and pump pressure vessel precharged 0.85 bar and assuming pump cutin/cutout pressures of 2.0/2.4 bar. The pump pressure vessel is tiny, probably 0.5L/1.0L, say 1.0L, at the pump cut out pressure of 2.4bar this little pressure vessel will now contain 0.46L of water and when the pressure falls to 2.0 bar it will contain 0.38L so there is only 80ML of water available between pump stop/start and thats why the pump starts instantly when any tap is even slightly opened. This is quite correct and normal operation IMO as that pump pressure vessel (anti cycling) is only designed to stop frequent pump stop/start when there is NO DEMAND for water, if the pump is frequently stop/starting say at night then either a tiny drip from a tap or the pump non return valve is passing. In short, the unvented cylinder E.vessel is purely for expansion purposes when the cylinder heats up and the pump pressure vessel acts purely as a mini anti cycling accumulator for the pump. Thats my story anyway.