On Sep 17, 11:24*pm, harry k wrote:
On Sep 17, 5:38*pm, "Dimitrios Paskoudniakis"
wrote:





"Paul Franklin" wrote in message

.. .

On Thu, 17 Sep 2009 19:20:23 -0400, Tony
wrote:

My bladder type water tank is rated 20 gallons.

With no water I have 26.5 lbs of air pressure in tank.

The pump cuts in at about 28lbs. and out at about 51lbs.

With the tank full I only get 6.75 gallons of water before the pump runs
again. *Is this right? *If not, what's wrong?

Thanks

If you check pressure tank spec sheets, they will specify the "Draw
Down" rating for the different size tanks and pressure switch
settings. *Draw down is the amount of water you will get between
cut-out and cut-in pressures.

A quick check of a brand or two on the web shows 20 gal tanks are
rated for about 6 gallons of draw down when using 30-50 settings.

So what you are seeing is about right for that tank with those
settings.

Switching to a larger tank will prevent the pump from cycling as
often, but you have to balance the capacity of your well and the run
time of the pump. *A larger tank means the pump runs longer (although
less often). *This can cause the water level in the well to fall below
the pump (low capacity well), and in extreme cases longer run time can
cause the pump to overheat.

Many of the tank and pump web sites have guidlines for sizing the tank
properly, but you need to know some details about your pump and well.
As tanks go, 20 gallons is pretty small.

HTH,

Paul F.

Get rid of the tank and go with a Grundfos variable speed pump and control
system. *It pressurizes in a small two-gallon tank while it pumps and only
operates on demand. *Variable speed means constant pressure. *If you set it
to 70 psi, turn on the washing machine, flush a toilet at the same time the
shower is on, the shower pressure is unaffected. *Try that with a pressure
tank. *I switched last year and I'm very happy.- Hide quoted text -

- Show quoted text -

Yes, but the drawback is sthat the pump runs _every_ time water is
drawn. *It is the start cycle that is hardest on pumps.

Harry K


Besides a variable speed pump, the other and more common way to
achieve constant pressure is with the use of a cycle stop valve which
works in conjunction with a small tank like the OP's 20 gal one.
Essentially it's a special valve goes between the pump and the rest of
the system and it maintains a constant pressure within a wide range of
flow rates. Say it is set to 50PSI. Then it works by throttling
back what the pump can deliver so the pressure is 50PSI whether you
are getting 2GPM or 12GPM. It will only allow a pressure higher
than the set 50PSI at flow rates BEKOW 1GPM. That is done to allow it
to then fill the tank up to whatever the cuttoff pressure is, which
might be 70PSI.

Which is better is a subject of debate among the manufacturers of the
two approaches. One thing is for sure, the cycle stop valve can be
used with a regular pump. A variable speed pump is a special pump
with more complexity, cost and controls required.

The operation of the OP;s tank sounds about right. The guidelines
for those kind of tanks generally call for the tank bladder to be
pressurized when empty and drained to 2PSI below whatever the cut-in
pressure is for the pump. So with a cut-in of 28, the tank should
be around 26. His is 26.5.