Navitron Renewable Energy and Sustainability Forum

Green Building and Design => Rainwater Harvesting / Grey Water Recovery & Processing => Topic started by: acresswell on July 26, 2015, 08:47:31 AM



Title: Pressure switch... Suppliers?
Post by: acresswell on July 26, 2015, 08:47:31 AM
Can anyone suggest where I can obtain a water pressure switch that I could plumb into a piece of 22mm pipe and which would switch on a pump when the pressure drops?

As has been documented elsewhere on this forum, (http://www.navitron.org.uk/forum/index.php/topic,23642.0.html), I have a rainwater pump that is pretty inaccessible in an underground tank.  This pump should have a pressure switch so it only runs when needed, but it seems to be running continuously so I suspect the pressure switch is faulty.  Rather than lowering myself into the tank, I'd rather fit a switch in the house where I can get to it.

Have tried obvious google searches like water pressure switch but without success...  Any suggestions would be appreciated.

Thanks!


Title: Re: Pressure switch... Suppliers?
Post by: Iain on July 26, 2015, 09:09:50 AM
Hi
Any use
https://www.machinemart.co.uk/shop/product/details/clarke-epc800-electronic-water-pump-control-un

http://www.ebay.co.uk/itm/151019-Automatic-Shower-Booster-Water-Pump-Pressure-Control-Adjustable-Switch-/291143709760?pt=LH_DefaultDomain_3&hash=item43c9847440

+ loads of others under water pressure switch

Iain


Title: Re: Pressure switch... Suppliers?
Post by: garethpuk on July 26, 2015, 09:35:44 AM
Pressure/level switch out of a washing machine any good? I played about with one out of our old washer and by blowing into the pipe I found it was adjustable from very low pressure to needing a good hard blow to switch.

Might be a silly idea but I thought I'd mention it ;D


Title: Re: Pressure switch... Suppliers?
Post by: bxman on July 26, 2015, 10:09:35 AM
Nothing silly about that very versatile and reliable


Title: Re: Pressure switch... Suppliers?
Post by: acresswell on July 26, 2015, 01:48:53 PM
Thanks for all those ideas, Iain.  Not sure how I missed all the ones on ebay.  I did try a search on there. Maybe I included 22mm as one of the search terms...

Washing machine pressure switch is a great idea.  Will look out for one before sending ebay any money!

Thanks again


Title: Re: Pressure switch... Suppliers?
Post by: acresswell on July 26, 2015, 11:01:34 PM
Have been looking on ebay at all the pressure switches. None of them seem to go any lower than 1.0bar.   I'm not sure if this is a problem, but it's not what I expected.

1.0bar (10m head of water) seems to be standard supply pressure from water board... but I don't think I need that much, especially as the pressure switch will be above ground floor level whereas they could be measuring 1m below ground level.  I only need about a 3m head to fill the upstairs toilet... so would ideally like to set the pump to come on when the pressure drops below 0.5 bar, and switch off when the pressure reaches somewhere over 1.0 bar.  Ideally I'd adjust it so that when the loo is flushed, the pump kicks in just once and then turns off before the cistern is completely full, relying on pressure in the system to fill the last little bit of the cistern... but without the pressure dropping below 0.5bar.  Don't want the pump to switch on and off a couple of times for each flush. 

I reckon a house with a water tank in the loft will often have barely 2m head (0.2 bar of pressure) to fill the bath, so 0.5 bar should be ample to quietly fill a cistern where flow rate is less of a concern. Does this make sense? 

Much of the pipework is speedfit, which claims to be ok to 12bar... but I'd rather not run it that high!

My gut reaction is that I want as big a difference as possible between the min pressure which triggers the pump and the max pressure that switches it off, so that the pump runs as infrequently as possible.  Does this make sense to other people or am I missing something?

Thanks



Title: Re: Pressure switch... Suppliers?
Post by: Iain on July 27, 2015, 08:47:09 AM
Hi
I run my rainwater system with a header tank and a float switch. Is that a possibility?

Iain


Title: Re: Pressure switch... Suppliers?
Post by: fatbob on July 27, 2015, 07:22:01 PM
My system suffered from pump hysteresis when I first set it up, it was cycling all the time.  Following helpful advice on the forum here I fitted an expansion tank between the pump (integral pressure switch) and the cistern and it all runs sweetly now.  The pressure switch on the pump is set to 30psi (2 bar).


Title: Re: Pressure switch... Suppliers?
Post by: sb79 on July 27, 2015, 10:51:39 PM
I use Square d or telemecanique pressure switches for booster sets (I think they are part of the same company theses days) which I get from a local hydraulic supplier for about 35-40 ish I think.


Title: Re: Pressure switch... Suppliers?
Post by: acresswell on July 28, 2015, 02:17:37 AM
I run my rainwater system with a header tank and a float switch. Is that a possibility?

Iain
Sadly not... all the pipework is already in place.  Running an extra pipe up into the loft (and another one back down) would just be too much disruption...


Title: Re: Pressure switch... Suppliers?
Post by: acresswell on July 28, 2015, 02:20:31 AM
My system suffered from pump hysteresis when I first set it up, it was cycling all the time.  Following helpful advice on the forum here I fitted an expansion tank between the pump (integral pressure switch) and the cistern and it all runs sweetly now.  The pressure switch on the pump is set to 30psi (2 bar).
I hope to be able to manage without the expansion vessel... there's quite a run of 32mm MDPE pipe between the tank and the house, so that may act in a similar way... but I had already planned to add in an extra tee to make it easy to add an expansion vessel later if needed.  How big is your expansion vessel?

Thanks!


Title: Re: Pressure switch... Suppliers?
Post by: oliver90owner on July 28, 2015, 09:05:44 AM
Using a pressure switch which is close to zero head, such as a washing machine pressure switch is a waste of time as the pump will switch on and off continuously - and the switch would need to be fitted close to the highest point to even operate.

Due consideration needs to be given to the pump pressure (and the receiving vessel safe limits, in the case of possible switch failure).  The normal situation is that of installing a (largish) expansion vessel which will allow extended water use before the pressure drops below the set point.

Repeated starts under load will destroy a pump motor, and is just as bad as (or probably worse than) a pump running continuously.


Title: Re: Pressure switch... Suppliers?
Post by: fatbob on July 28, 2015, 06:08:29 PM
My system suffered from pump hysteresis when I first set it up, it was cycling all the time.  Following helpful advice on the forum here I fitted an expansion tank between the pump (integral pressure switch) and the cistern and it all runs sweetly now.  The pressure switch on the pump is set to 30psi (2 bar).
I hope to be able to manage without the expansion vessel... there's quite a run of 32mm MDPE pipe between the tank and the house, so that may act in a similar way... but I had already planned to add in an extra tee to make it easy to add an expansion vessel later if needed.  How big is your expansion vessel?

Thanks!

Mine's only a wee little thing Fiamma A20, maybe about a litre at the most, but I think some here have fitted quite big ones to reduce the number of pump operations.  I'm thinking the bore of pipework from the tank/pump to the pressure switch won't make much difference expansion wise, it's only on the section of pipe between the pressure switch and your outlet/cistern that would act as an expansion medium as that's the section that is having it's pressure monitored.  Hence your expansion vessel if you fit one would need to be on this section of pipe also.  But that said I'm no expert, just going on what worked for me, others I'm sure will be able to correct me if I'm wrong  ;D


Title: Re: Pressure switch... Suppliers?
Post by: sb79 on August 12, 2015, 10:53:39 PM
I doubt if this is going to operate correctly without an expansion vessel. It'll be in hysteresis all the time. For the cost of a vessel (40 or so for a 25ltr potable vessel) I think you should be fitting one as a matter of course. Just make sure it is a potable water one rather than a central heating one...


Title: Re: Pressure switch... Suppliers?
Post by: acresswell on October 17, 2015, 08:14:45 AM
How do expansion vessels cope with freezing?

I delayed adding an expansion vessel because there wasn't space for a sensible size one to go under the kitchen sink where the rest of the valves, etc, were going.
Now wish I had because the pump has died.

But I've just had what might be a brainwave...  ;D
 
The rainwater pump also supplies an outside tap, with the pipework tee'd off under the kitchen sink before running through the garage.  Is there any reason why the expansion vessel would need to be where the rainwater enters the house, or can it go anywhere on the pipework?  I could put the expansion vessel in the garage, but there is a small risk that the temp could drop below freezing.  Never had any problem with frozen pipes in the garage, but would this destroy the expansion vessel if it happened?


Title: Re: Pressure switch... Suppliers?
Post by: fatbob on November 01, 2015, 07:33:25 PM
Quote
How do expansion vessels cope with freezing?

Not sure ! Mine's in the garage but has not been through a freeze as yet.  My filters and pump are also in the garage...must get around to insulating it all like I promised myself back in spring lol  ;D Would assume as the tank has a diaphragm inside, it would flex and cope with with ice expansion ?

Can't think of a reason why the location of the expansion tank would be a problem - as long as it's in there somewhere it would maintain the pressure in the pipework as a whole ?  I'm no expert in hydraulics tho.


Title: Re: Pressure switch... Suppliers?
Post by: dickster on November 02, 2015, 11:43:28 AM
Hi, I fitted a Hozelock garden pump in a box above ground which sucks from 2m deep old septic tank. Bolted a 50.00 Machine Mart pressure switch on top. No expansion vessel. Both toilet and washing machine now successfully supplied. After initial pumping, pump switches on and off again once for about 7 secs after each use. The box is well insulated and I am hoping that the 100mm ducting between tank and box will allow the warmer air warmed by the water in the tank to keep the pump from freezing up. No real frosts yet, so fingers crossed.


Title: Re: Pressure switch... Suppliers?
Post by: DonL on November 04, 2015, 04:53:46 PM
I've been scratching my head to remember the name of a company I used to use who made robust and sensibly priced pressure switches including low ranges. It's finally come back to me and they seem to be still trading http://www.baileymackey.com/pressure%20switches/switchintro.html
Don


Title: Re: Pressure switch... Suppliers?
Post by: sb79 on November 09, 2015, 07:35:38 PM
If the vessel is in an unheated area it will need insulating. I have replaced numerous vessels over the years due to frost damage, usually people just leave them in the open and then wonder why they've no water at some inconvenient time.....

Inside an insulated box or wrapped with knauf space blanket (other products are available) or even old duvets?

The pressure switch I like to use is the square d 9013 and I tee in a gauge (usually jet range one from plumb center- other makes are available) between switch and vessel.