Secondary return with an already pumped system.

BW2

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The system is vented with a tank in the loft.

New bathroom (shower, basin, WC) going in - also in the loft – so going to be negative head pumping for all of those.

But, the bathroom is 16m of 22mm pipe away from the tank, so I’d have to run off a gallon every time, to get the first dribble of HW coming through.

How can I do a secondary return to get over this with an already pumped system. If I put in a secondary pump to get the HW to the taps, then it’s flow would kick the main pump into action? and that would then be driving the secondary pump. Then there’s got to be a way to stop the recirculation when enough HW has got to the taps.

Is there some way I could get the main pump to do the recirculation? Open the tap to get the main pump started, but the water can recirculate back to the tank until a temperature-controlled valve near the taps senses hot & closes off the return?
Would it work?
Do they make such things?
Is there a ‘proper’ way to do it?
 
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It is technically possible, although I wouldn't guarantee it.

A negative head pumps works on pressure loss, so in theory you could install a secondary circuit and feed the booster pump as a dead leg from the circuit pipework, you would need check valves on the cylinder side of the connection, and you could possibly starve the pump, and create any number of unknown problems.
 
Dear Doitall – thanks for your reply.

Not sure I explained it very clearly – cleared it a bit more in my own head now.
Would the following work?

Just have the one pump (the negative head booster pump). As normal, it goes to the bathroom & gets switched on when a tap is opened & the water starts to flow.

But then add a return leg from the bathroom to the cylinder ( ie just before the first bathroom tap, on the HW supply add a sidebranch going to a temperature-controlled valve that then goes back to the cylinder).

For most of the time, no taps are open, no water is going anywhere. The TCvalve is cold and therefore open.
When a tap is turned on, the booster pump switches on & starts to pump HW along the pipe. A little goes out the tap, but most of it goes through the open valve and returns to the cylinder.
When the hot water gets through to the bathroom, the TCvalve closes. A second later HW comes out of the tap.

What’s a check valve & how would I use it??

Regards BW2
 
You will have a non return valve (check valve) in the pump discharge with a negative head pump and the moment you return a secondary loop back to the cylinder you will lose the charge in the expansion vessel and the pump will run constantly as no pressure will build up in order to activate the pressure switch!
I don't think it will work.
 
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correct if you think this is wrong or won't work

but my theory is

1. tank or incoming service

2. single check valve

3. cylinder

4. Surrey flange for return to enter cylinder

5. pipe to bathroom. vvvvv ........ ^^^^^circulator

6. tee for return to exit vvvv>>>> .........^^^^^return pipe

7. negative pump

8. taps in bathroom

now if pump pressurises, the circulator can still run. but the neg pump will be satisfied so will stop until tap opens and pressure drops.
EDIT: vvvvv = flow .......... ^^^^^= return (does that make it clearer?)
 
That's basically a list of components and difficult to visualise what goes where without a drawing. :(
 
not that difficult

as all it consists of is a supply to cylinder via cold feed
a cylinder with a surrey fitted inthe hot outlet
a pipe to the bathroom with a return incorporating a circulator
then a neg pump prior to taps after return is taken off
 
If you have taken a secondary return pipe from the taps back to the cylinder then this will de-pressurize the expansion vessel and pump will fire up constantly.
 
how ? if the return is prior to the pump surely the expansion would be after the pump :confused:

edit: maybe my understanding is wrong on how these pumps work!
 
The pump will be located close to the cylinder.
The OP has 16M of 22mm pipe after the pump which is pressurised!
 
Dear Doitall – thanks for your reply.

Not sure I explained it very clearly – cleared it a bit more in my own head now.
Would the following work?

Just have the one pump (the negative head booster pump). As normal, it goes to the bathroom & gets switched on when a tap is opened & the water starts to flow.

But then add a return leg from the bathroom to the cylinder ( ie just before the first bathroom tap, on the HW supply add a sidebranch going to a temperature-controlled valve that then goes back to the cylinder).

For most of the time, no taps are open, no water is going anywhere. The TCvalve is cold and therefore open.
When a tap is turned on, the booster pump switches on & starts to pump HW along the pipe. A little goes out the tap, but most of it goes through the open valve and returns to the cylinder.
When the hot water gets through to the bathroom, the TCvalve closes. A second later HW comes out of the tap.

What’s a check valve & how would I use it??

Regards BW2

No you will blow the cylinder up, or should I say you will empty the cylinder in the storage tank.

The only possible way is to install a secondary loop with a bronze pump, and feed the booster from the loop.
 
Doitall wrote

The only possible way is to install a secondary loop with a bronze pump, and feed the booster from the loop

That's meaningless to the OP.
Lets have a diagram Doitall.
If I knew what you was on about I would post your design up in a clear schematic. :rolleyes:
 
Doitall wrote

The only possible way is to install a secondary loop with a bronze pump, and feed the booster from the loop

That's meaningless to the OP.
Lets have a diagram Doitall.
If I knew what you was on about I would post your design up in a clear schematic. :rolleyes:

You do know what a secondary loop is. A pipe that come from the cylinder goes around the building and ends up with a bronze pump and a check valve to stop back circulation when a tap is open.

The booster would have to connect as a dead leg from the loop.

Draw a big circle, place the cylinder somewhere in the middle of the pipes, and have the bronze pump circulating the water. Next insert a tee for the hot water to the bath, cut the pipe in half and connect the booster pump.
 
Doitall wrote

The only possible way is to install a secondary loop with a bronze pump, and feed the booster from the loop

That's meaningless to the OP.
Lets have a diagram Doitall.
If I knew what you was on about I would post your design up in a clear schematic. :rolleyes:

You do know what a secondary loop is. A pipe that come from the cylinder goes around the building and ends up with a bronze pump and a check valve to stop back circulation when a tap is open.

The booster would have to connect as a dead leg from the loop.

Draw a big circle, place the cylinder somewhere in the middle of the pipes, and have the bronze pump circulating the water. Next insert a tee for the hot water to the bath, cut the pipe in half and connect the booster pump.

that is exactly what i said the only way is for the pump to be after the secondary loop

there is possibly one other way and that is to put an unvented cylinder in then you could pressurise the cylinder and pipework.
 

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