[RE-wrenches] Wireless control of off-grid pumps

Matt solarone at charter.net
Wed Sep 3 17:33:44 PDT 2008


Hi Windy,

And, just to make this conversation more complicated, Monoflo solar pumps (which we distribute - but I am not attempting to sell here) have another way of approaching this problem. The SMC (Solar Motor Controller) for the Monoflo can be programmed to shut the pump off when the line pressure exceeds a preset level without the need for external pressure switches or expensive "snap" valves. All that is needed is a standard tank valve.

When the pump shuts down, the controller waits for 30 minutes and attempts a restart. If the water has fallen in the tak enough to relieve the line pressure, it will pump until the pressure rises again, and the process is repeated. This method works very nicely in systems with very long pipe runs (I know of one >3 miles long) nad no external sensors are needed.

Added to this are several other nifty features, such as programmable pump speed control, solar input and low water shutoff recharge times.

All very nice!

Matt
---- Windy Dankoff <windydankoff at mac.com> wrote: 
> Hey Allan,
> 
> Remember me?  :-)
> 
> Roy's suggestion of using a float valve at the storage tank to actuate  
> a pressure switch near the pump can be feasible under the right  
> conditions.
> 
> As William says, you need a valve that will snap shut, not float up  
> slowly. Here is one that is cheaper than the one he suggests, and made  
> here in USA:
> http://hudsonvalve.com/products.html
> 
> I don't see where they describe its snap action, but that's how it was  
> described to me. I tested one and it did a snappy job. Cheap too.
> 
> Next problem is pressure switch. A standard switch like a Square-D or  
> similar will work reliably down to a setting of roughly 20 PSI cut- 
> out, from my experience, and an on/off differential of maybe 5 PSI? (I  
> don't know, but it will work somewhat lower than its rated range).  
> Anything more sensitive than that may be exotic and expensive. The  
> pump must be capable of producing sufficient pressure (briefly) to  
> trigger the pressure switch, whatever switch you choose. If the pump  
> is a positive displacement type (like the lower volume, high-lift SQF  
> pumps), then there's no problem producing sufficient additional  
> pressure to work a standard pressure switch unless the pump is already  
> working to its limit of pressure.
> 
> I've always recommended using a small pressure tank at that pressure  
> switch (just like in a normal pressurizing system). It absorbs water  
> hammer and prevents rapid chatter of the switch.
> 
> I wish I had some documentation, but I can only say that I've  
> recommended this method to many customers who had no other good  
> choice. I know some of them did it, and I never heard of any problems  
> when done right.
> 
> Yours,
> Windy
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