Control of 2 pumps conundrum

[sargan]

Hoping someone can spot something simple.
I have 2 pumps, that I never want to operate at the same time.
In the link I have attached a drawing of my thoughts … at bottom of post and aslo on this link:

http://tinyurl.com/z2eoz9u

Condition 1. Programmer in Timed=OFF
No live to Heating Ctl board, and no power to pump BP. If flow switch operates, then RLY (after time T) will operate and put power onto pump SP via connection (2b) … all fine

Condition 2. Programmer in Timed=ON
Provides live to heating controller … and in the event of it calling for heat will provide a switched live feed from ‘pump ’ and I can use that to power the boiler pump BP, via RLY connection (1a)
There are a number of thermostats, zone valves etc. all under control of Heating Control board so can only run pump BP when there is a 'Pump' live signal.

If the flow switch operates when boiler is making a heat call, I need pump SP not to operate, as there would be no power to (2b) that requirement is met

The issue I have is if there is no call for heat and flow switch operates I need pump SP to run … so I need to get live feed to it at that point ……… currently stumped.
Am I missing something that I can achieve given the DPDT contacts in relay and SPDT in the programmer.
Otherwise I will have to add in another RLY


Ideas welcome.

 

[ShaunCorbs]

can i ask why do you need two pumps?

 

[SimonG]

2 two ports with micro switches.

 

[sargan]

One pump is normal boiler pump .... the other is a shunt pump to provide de-stratification of thermal store when main boiler control system will be powered off in summer months.
Without this the heat exchanger in store will not have a flow of hot water over it.

In summer heat input will be by Solar PV array via Inverter switch to immersion (free power) so boiler will be off

 

[sargan]

I don't want to add anymore valves, if you mean add 2 2 port valves

 

[Jay The Plumber]

I cant see a way to do it without adding a relay or creating a logic condition where the output of the flow switch runs through an existing zone valve microswitch for example where the logical condition is that the flow switch would never operate without the zone valve being in that position.

 

[sargan]

I can see how to do it with another relay - just wanted to make sure I was not missing something simple.

 

[Howsie]

Why PV over ST btw?

 

[Jay The Plumber]

I can see how to do it with another relay - just wanted to make sure I was not missing something simple.

if you are, so am I

 

[Jay The Plumber]

what happens if flow switch operates while there is a call for heat?
pump BP will have it power cut, is that a problem?

 

[sargan]

You are right ... another issue for me ... if there is call for heat ... and the flow switch operates I would need pump BP to run and not pump SP


The system manufacturer said just wire in shunt pump to flow switch ... on occasions when both bumps could be active would not be an issue worth worrying about.

I'm just trying to think it through a bit more and get only one pump active at any time.
So still have my initial issue to resolve.

 

[sargan]

OK ... can't find a way to do it with just the timer spst switch and the dpdt relay.

Needed a separate switch ... easiest & cheapest (~£3), seems to be to add a 2nd relay, which the allows creation of 'if' and 'THEN' logic.
i.e. IF pump BP running THEN block Flow switch signal:

 

[Jay The Plumber]

so if timer is on and there is no call for heat, you still wont get SP to fire as the timer isnt supplying a live to connection RLY (B1)

do you have any spare contacts on RLY 1?

 

[Jay The Plumber]

had a quick look and I think you can supply connection RLY2(B2) from "Timed On" connection and then take that parallel connection to pump SP

 

[Jay The Plumber]

sorry for the poor modification, im on my laptop but that should do everything you want

 

[sargan]

you are right ... well done that man.

 

[Jay The Plumber]

Welcome!

 

[sargan]

updated as per your suggestion ......... well spotted, missed that combination.

 

[Jay The Plumber]

what are you using to CAD the schematic up ?
I have an old version of CAD but its a real PITA to use for schematics.

 

[sargan]

It's just a basic 2D drawing programme, used it for years .. Visio
I just drew using basic shapes..
It has extensive templates for schematics for electrical, mechanical, hydraulic, room layouts, business org charts etc.
Very intuitive & simple to use.