"off the grid" Pump System

I am at my father in laws on the big island of Hawaii right now. He is set up with an "off the grid" system. He collects his water from the rain and uses solar for power. He uses a LP Gas instant water heater (Paloma Brand).

He was having some difficulty with the water main heater cutting out specifically while using the shower. I have played with his system some and discovered that it does not work well under 40 lbs, but is fine over. I read in the manual and found a note that said for this particular unit the system should be set to 40/60 water pressure it also says that any restricters in shower heads should be removed and I did this which helped a little. His pump is a low HP unit because of power draw so the highest pressure I can get out of his pump is 50 lbs. which again works fine as longs as it is above 40. What I tried to do is to adjust the pressure switch so that it would cut in at 40 and off at 50, but had some trouble doing this. I set the cut in pressure (larger nut) at 40 and then tried to lessen the gap by backing off the smaller nut, but I backed off the smaller nut until it was completely de-sprung. the smallest gap I can seem to set is 20lbs so right now it is set to 30/50. any more would over work the pump and draw too much power and eventually kill the pump.

The note in the manual is a little strange because the data sheet says that it should be able to handle down to something like 4 lbs of pressure, but then it has this strange note some time later. Im not sure where to go from here. Im thinking the pressure switch should be able to set at 40/50, but I dont know why I cant get it. It is a standard square D type. I might just try to buy a new pressure switch but wanted to ask first because Im not sure this would change anything and we are on a budget.

If you can lend any advice on this matter it would be appreciated,

Thank You,

Wilson D

Standard switches usually won't come down more than 17 lbs. Trying to get a 10 lb differential is virtually impossible. I think Square D does make such a switch, but it won't be on the Hardware's shelf. You would have to go looking for one.

The other problem is setting the switch to the pumps max pressure. If the water level changes by just a foot or so, the switch setting will make it impossible for the pump to shut off, which will result in nuked fittings and pump parts.

bob...

It is flow and not pressure that triggers the water heater. When you get down to low pressure, the shower head is not putting out enough flow to trigger the heater. Try taking off the shower head, and see if the water heater stays on. Removing the little water saver washer from the shower head is a good start but, you may have to drill out the holes in the shower head to get the flow needed when the pressure is low.