Soft Start?

[Bob_T]

From reading through the information on the Cycle Stop valves I have the impression that they will also act as a soft start for the pump, evidently by restricting the initial flow when the pump starts.  Maybe I'm mistaken.

However, given a pressure switch setting of 40 and 60 psig and a Cycle Stop valve setting of say 50 psi, here is what I don't understand.
Say the pump is off and the tank is at 60 psi when a sprinkler system is turned on.  They sprinklers have a demand higher than the pump can keep up with.  As the pressure drops below the 50 psi Cycle Stop setpoint, I'm thinking that it will open up and when the tank pressure reaches the 40 psi pump start pressure, the Cycle Start valve will be wide open?  Can you please explain how the Cycle Stop approximates a soft start condition?

Edit: I think I found my answer in another thread here.  The Cycle Stop valve evidently is not wide open when the pump starts and is partly closed and limits the initial flow.   I'd still appreciate any comments you may have.

Thank you,

Bob

[Cary Austin]

2” and larger CSV’s are normally closed.  This means they are in the closed (5 GPM) position when the pump starts, no matter the pressure setting. 

The smaller, direct acting CSV’s are normally open.  This means the only thing that holds them closed (1, 2, or 5 GPM) position is when the downstream pressure is higher than the valves set pressure.  So with a 40/60 pressure switch, the CSV would need to be set at 40 PSI to be in the closed (1, 2, or 5 GPM) position when the pump starts.

However, the water in the well pipe is still holding pressure on the pump in the well, along with the 40 PSI in the tank as the pump starts (40/60 switch, CSV at 50).  As water is not compressible, and the CSV reacts instantaneously, the first wave of water coming from the pump will actually close the CSV for and instant.  This blocks the pressure wave from traveling further than the CSV.  The CSV instantly starts controlling the pressure, if it is higher than the set point.  Or opens up fully if the pressure is below the set point.  Either way the CSV prevents any pressure pulse further down the line. 

This is not quite as good for a soft start as being in the closed position like the larger CSV’s are.  Although I don’t think soft start is nearly as important on a 10 GPM pump as it is a 100 GPM pump.  You can also get a reduced voltage soft start by using the longest length of the smallest wire possible for the horsepower motor that you have.  Franklin says, “using the maximum recommended cable length there will be about 20% reduced starting current and about 36% reduced starting torque”.   Basically, over-sizing the pump cable is not a good thing, as the right size cable can give you all the benefits of a reduced voltage soft starter.

All Cycle Stop Valves, large or small, will be in the “closed” (or minimum flow) position when the pump stops.  This certainly gives you a soft stop, as the check valve is only open the thickness of a piece of paper at these low flow rates.  So when the pump shuts off, the check valve “kisses off” quietly, and water hammer is completely eliminated.

[Bob_T]

Interesting about the cable length.  I've been thinking sort of the same thing.  The cable now is 8 gage and about 470 feet long, which I think is exactly Franklin's maximum recommended length for this pump/motor.

Thanks,

Bob

[Cary Austin]

Yep.  3 HP, #8 wire to 470'.  You already have your soft starter.