Help me understand this pump curve

jiran79 · Apr 3, 2023

This pump curve is from a combi boiler with an internal automatic bypass valve.

Why is the maximum flow obtained with the bypass valve in the middle position? Shouldn't a fully closed bypass valve result in a higher flow through the main circuit?

Also, any idea what 'V1' and 'V2' mean (no clues in the boiler manual)?

ShaunCorbs · Apr 3, 2023

V1 and v2 boilers ??

Also the bypass won’t operate until the pressure is overcome so probably had a higher pressure spring than the pump force on an open circuit

jiran79 · Apr 3, 2023

Could V1 and V2 have any special meaning besides versions of this particular model?

I follow your sentence about the bypass operation, assuming it is some type of spring loaded valve. But this does not explain the curves. The blue, red and black curves must have been generated with the valve held into a particular position and in this situation I would expect the red and black to be swapped.

John.g · Apr 3, 2023

Some Vaillants mention one step and 2 step pumps. This is from a Ecotec 630.

jiran79 · Apr 3, 2023

Difficult to be certain, but I think this pump is single speed.

John.g · Apr 3, 2023

All modern pumps are variable speed with different modes/settings, you could have 3 CC settings, 3 PP settings and 3 CP settings, each of these will have a different closed valve (dead headed) head so perhaps something like that.

jiran79 · Apr 3, 2023

The boiler is a Heat Line Monza, if this helps.

John.g · Apr 4, 2023

Had a scan through that but really none the wiser, it states that the bypass is automatic and non adjustable which probably means just a spring loaded bypss so the pump speed is controlled automatically to give a certain by pass based on operating conditions like flow/return dT etc. The pump curve only gives one V1 curve (bypass closed), also don' know what 35W means on all curves, 35W would be a typical A rated pump power.
Other info is that the 24kw boiler max outputs are 17.6kw/24kw, heating/DHW and the 28kw boiler max outputs are 23.4kw/28kw, heating/DHW but with probably the same circ pump.

Ric2013 · Apr 4, 2023

John.g said:
All modern pumps are variable speed with different modes/settings, you could have 3 CC settings, 3 PP settings and 3 CP settings, each of these will have a different closed valve (dead headed) head so perhaps something like that.

If the pump is integrated into the boiler, this may not be possible to adjust. Perhaps the boiler manufacturer saw fit to have the pump made so as to only operate in one mode?

Ric2013 · Apr 4, 2023

jiran79 said:
The blue, red and black curves must have been generated with the valve held into a particular position and in this situation I would expect the red and black to be swapped.

Proportional pressure pump set to increase head with flow might, hypothetically, send more flow around system with the bypass open, though seems unlikely.

John.g · Apr 4, 2023

You can set up a pump in PP mode with a fixed springloaded ABV to pass a certain flow but as system demand increases so too does the pump head in PP mode which forces the ABV to recirculate more, the opposite to what you require, thats why PP mode is not recommended for external ABVs, constant curve (fixed speed) mode was traditionally the proper mode but all modern pumps now control a good portion of their flowrate in a constant pressure fashion even when running in PP mode, the UPS3 is one of the best (or worst) examples of this.
Its likely IMO that the above pump control is done in PWM mode where invinitely adjustable speed is used depending on the flow and boiler temperature conditions, especially the flow/return temperatures dT.

Ric2013 · Apr 5, 2023

PWM? (And I'll use the extra letters to complain about acronyms)

John.g · Apr 5, 2023

Pulse Width Module, 0 to 10V.
Search with PWM or/and go to page 14.

Chuck · Apr 5, 2023

jiran79 said:
I would expect the red and black to be swapped.

I agree, the graph key has been muddled up. I think you have a simple pump with two speeds (V1=black, V2=green) and a simple bypass valve that can be closed, part-open (red), or fully open (blue). There'd be no point using V1 with the bypass open as it would essentially give the same performance as the green and red curves but use more electrical power in the process. I suspect that the V1 setting will use more power, say 45W rather than 35W.

These are the sort of errors that get introduced when technical graphs from engineers are 'redrawn for publication' by non-engineers.

Help me understand this pump curve

jiran79

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