Auto bypass always open - help!

[chris watkins]

Don't you need the bypass to prevent the pump getting dead headed on the pump overrun?

Pump reads the increase in pressure and just slows down to 5Watts.
But if boiler does need to clear away heat then yes.
Forgot my one always has open circuit as I have WC.

 

[Chris Clarke]

Something like this?

 

[chris watkins]

Yes just like that.
Good old Andrew M he pointed the way for me, also have a look at Caleffi - section 5 Page 27
https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_15_na.pdf

 

[doitmyself]

Thanks, makes sense to me. Although is 3.5m head sufficient for the longest microbore to manifold circuit of 18m? My rough calculations would suggest not.

It's not just the length of the pipe which is important. You have to take into account the flow rate, which depends on the size of radiator and the temperature differential. For example:

Resistance of 18m of 10mm pipe connected to a 2kW rad with a 20C differential is approx 0.58m, with a 10C differential it is approx 1.94m. The flow rate has doubled so the resistance increases by four times.

Upload your rough calculations and I can take a look at them.

 

[Chris Clarke]

So presumably the two pumps are wired to the same point and both overrun? The intelligent pump shuts down itself when the valves close?

 

[Chris Clarke]

It's not just the length of the pipe which is important. You have to take into account the flow rate, which depends on the size of radiator and the temperature differential. For example:

Resistance of 18m of 10mm pipe connected to a 2kW rad with a 20C differential is approx 0.58m, with a 10C differential it is approx 1.94m. The flow rate has doubled so the resistance increases by four times.

Upload your rough calculations and I can take a look at them.

It's not just the length of the pipe which is important. You have to take into account the flow rate, which depends on the size of radiator and the temperature differential. For example:

Resistance of 18m of 10mm pipe connected to a 2kW rad with a 20C differential is approx 0.58m, with a 10C differential it is approx 1.94m. The flow rate has doubled so the resistance increases by four times.

Upload your rough calculations and I can take a look at them.

I won't embarrass myself as they are obviously wrong and too basic. It's plastic pipe too which might make a difference?

 

[Ben Slade]

Won’t the flow go straight through the bypass valve as it is on its max setting now and it would have the path of least resistance than the rest of the system?

 

[Chris Clarke]

Won’t the flow go straight through the bypass valve as it is on its max setting now and it would have the path of least resistance than the rest of the system?

Hi Ben,

I might be wrong but I think the hydraulic separation using close coupled tees would mean the bypass could be removed.

 

[Ben Slade]

Hi Ben,

I might be wrong but I think the hydraulic separation using close coupled tees would mean the bypass could be removed.

Right I’m with you! Cheers for the enlightenment.

 

[Ben Slade]

Are you going to use both the tees and the hydraulic separation I was under the impression it’s one or the other with the tees being the cheapest?

 

[chris watkins]

Hydraulic separation of the boiler from the system is achieved by using a CCT's or LLH

 

[chris watkins]

I won't embarrass myself as they are obviously wrong and too basic. It's plastic pipe too which might make a difference?

Not wrong just has advantages / disadvantages = smoother bore less fitting but at the end of the days it is a small pipe which limits the heat flow to each rad to something like 3 - 3.5kW but each is fed directly from a 22mm manifold.

 

[Ric2013]

To highlight a commonly held misconception that a differential pressure automatic bypass valve works well with a proportional pressure pump (e.g. Grundfos Autoadapt), please note that Grundfos does not recommend that the two are used together.

 

[fezster]

Indeed: http://www.newtonnet.co.uk/permanent/GrundfosDocs/BypassCommissioningAlpha2or2L.pdf

A fixed bypass is a manually adjusted valve which is set to give the required bypass flow. It could be a simple valve, but Grundfos recommends the use of the Taco Nova Setter valve with flow gauge.

 

[Chris Clarke]

Thanks for the extra info. I hope to update this thread once I have (hopefully) found a solution.