Triggering a pump in a negative head system

[pmx_super]

I was wondering.. if the manufacturer's spec for a shower pump states that the shower head much be at least x amount below the bottom of the cold supply tank would it work to just turn on the shower with the shower head on the shower tray floor (provided it's low enough) to trigger the pump, then put it back up above head-height?

Also, what is it triggers the pump? Pressure or flow? Reason I ask, I'm wondering whether a pump on the hot supply to a venturi shower mixer would be more likely to trigger due to the 'negative pressure' generated by the venturi system?

 

[Rico99]

Hi there,

You don't need a pump to a venturi shower.

It uses the mains pressure/flow rates to "pull" the hot thru faster.

Rico

 

[pmx_super]

Hi there,

You don't need a pump to a venturi shower.

It uses the mains pressure/flow rates to "pull" the hot thru faster.

Rico

Sadly I do because they don't perform well enough for a negative head situation.

Path of least resistance seems to be pumping the hot. Path of cheapest resistance to be using a positive head pump. I'm also hoping that by using a positive head pump it'll stop the pump from triggering when any of the other hot outlets are opened.

 

[Rico99]

Hi there,

Is the cold supply definatley off the main.

Not sure what damage could be done to the shower if you pump the hot.

I still don't think it would work if oyu pumped the hot as the shower needs the mains pressure to "pull" the hot thru.

I think your best bet is speaking to maker of the shower and see ehat they say.

You may need to change the shower completely.

Do you have a cwsc in the loft. Maybe you could re-do pipework from there and from cylinder and fit pump for both supplies.

Rico

 

[pmx_super]

Hi there,
Is the cold supply definatley off the main.

yes

Not sure what damage could be done to the shower if you pump the hot.

Why did it occur to you that it may damage the shower? What is there to damage?

I still don't think it would work if oyu pumped the hot as the shower needs the mains pressure to "pull" the hot thru.

It'll still have mains pressure (weak as it is). Hot will just be pushed harder than it's currently being pulled.

I think your best bet is speaking to maker of the shower and see ehat they say.

You may need to change the shower completely.

Good idea!

Do you have a cwsc in the loft. Maybe you could re-do pipework from there and from cylinder and fit pump for both supplies.

trying hard to avoid this option - no loft - it's a flat. Access is hellish.

 

[Rico99]

Hi there,

Do you know the pressure / flow rate of you cold mains.

As you are in a flat is it a shared supply with rest of building, or do you have your own supply pipe.

Rico

 

[Rico99]

Hi there,

Just been looking at Trevi Website.

Their Venturi will work with neg head hot, but clod pressure must be between 1.5 & 3.0 bar, otherwise they are not suitable.

Rico

 

[Redhotferrari]

If you are going down the road of a pump, why pay all that money for a venturi shower, the reason to fit one is so you dont have to fit a pump.

Best wet might be to fit a negative head pump and a normal mixer

 

[Rico99]

If you are going down the road of a pump, why pay all that money for a venturi shower, the reason to fit one is so you dont have to fit a pump.

Best wet might be to fit a negative head pump and a normal mixer

Problem he has is that Cold Main pressure is pi$$ poor so won't activate venturi. And he doesn't have CWSC to use to install te pump.
OP wants to pump the hot supply to the Venturi but I dont think he can do that.

Rico

 

[pmx_super]

I do share the cold main with the rest of the building. Yes the pressure is **** poor, which certainly has something to do with the poor performance of the Venturi unit. I get about 10 l/min when I turn the shower head to cold.

I'm still not sure why you think I can't pump the hot into the venturi mixer.. what do you think will go wrong?

 

[Rico99]

Hi there,

Just spoken to Trevi (their venturi is the boost) the techincal support told me that pumping the hot would make not difference to the perfomance fullstop.

It HAS to have the mains cold pressure to "pull" the hot through.

Rico

 

[pmx_super]

Hi there,

Just spoken to Trevi (their venturi is the boost) the techincal support told me that pumping the hot would make not difference to the perfomance fullstop.

It HAS to have the mains cold pressure to "pull" the hot through.

Rico

Thanks for that..it's just so counter-intuitive to me that increasing hot pressure won't increase hot flow. They're also pretty adamant on their website that it's only for 0-0.3bar head on the hot feed, though the graphs shown suggest performance improves, irrespective of cold pressure, as the hot pressure increases upto 0.3 bar.

Anyway.. I'm pretty convinced a new mixer would be required. So, original question just without the venturi bit. Can I trigger the pump by sticking the shower head on the floor?

 

[Rico99]

It depends on the type of pump as neg head and pos head pumps work in different ways.

One works off flow and the other of pressure.

Are you thinking of pumping both supplies or just the hot as per your other posts.

Rico

 

[pmx_super]

It depends on the type of pump as neg head and pos head pumps work in different ways.

One works off flow and the other of pressure.

Are you thinking of pumping both supplies or just the hot as per your other posts.

Rico

Just pumping hot.

Naturally pumping both is the ideal solution, but would sadlly cost me a fortune.