Could this be?
Could this be?
(OP)
I have a simple weighted arm swing check, 8-inch, horizontal installation, resilient seated, NOT installed as a check (not intended to prevent backflow). The valve opens in the direction of flow and is bypassed by a two-inch connection (18-feet sched. 40, two ells, one magnetic flow meter and one injection tee, all 2-inch). The arm and weight have been modified so the valve opens when 1.7 PSI of differential is developed - by flow through the 2-inch.
When flowing more than 50 GPM or when not pressurized, the valve arm, and valve disc, opens freely, with manual lifting of the weighted arm. When only pressurized (90 PSI) and not flowing, lifting the arm becomes very difficult, initially. A coworker suggests, and I agree, that the 90 PSI is acting on different upstream and downstream areas. That is, the upstream pressurized area (tending to open the valve) is the inside diameter of the seat opening, while the downstream pressure is acting on the area of the opening plus the seating area of the resilient seat. This makes the upstream area, D=8” while the downstream area is D=8 1/8” or 8 1/4 “. The difference in area is 1.9 to 3.2 square inches and the difference in force is, at 90 PSI, 171 to 280 pounds. Does this seem reasonable?
Thanks
Steve
When flowing more than 50 GPM or when not pressurized, the valve arm, and valve disc, opens freely, with manual lifting of the weighted arm. When only pressurized (90 PSI) and not flowing, lifting the arm becomes very difficult, initially. A coworker suggests, and I agree, that the 90 PSI is acting on different upstream and downstream areas. That is, the upstream pressurized area (tending to open the valve) is the inside diameter of the seat opening, while the downstream pressure is acting on the area of the opening plus the seating area of the resilient seat. This makes the upstream area, D=8” while the downstream area is D=8 1/8” or 8 1/4 “. The difference in area is 1.9 to 3.2 square inches and the difference in force is, at 90 PSI, 171 to 280 pounds. Does this seem reasonable?
Thanks
Steve





RE: Could this be?
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Could this be?
Katmar Software - Uconeer 3.0
http://katmarsoftware.com
"An undefined problem has an infinite number of solutions"
RE: Could this be?
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Could this be?
I think that the 90 PSIG (same on both sides) is operating on unequal areas, with the downstream area being a little larger. The initial manual lifting of the arm removes some slop in the keyway and the encounters the breaking force required to overcome the differential force.
Is this possible?
Thanks
Steve
RE: Could this be?
When there is no differential pressure across the valve and you have 90 psi both sides, then the seal is compressed and the diameter of the contact area could increase to 8 1/8" or more, giving the 171+ pounds you originally calculated
Katmar Software - Uconeer 3.0
http://katmarsoftware.com
"An undefined problem has an infinite number of solutions"
RE: Could this be?
I don't have an answer but I do have two more questions.
Is the piping horizontal or vertical? (can there air trapped under the check valve?)
Is there a check valve in the 2" branch piping that stops water from flowing backwards during the "no forward flow" situation?
Thanks
Stonecold
RE: Could this be?
I think you and I agree. I am not interested in the cracking pressure during normal flow conditions, just now only in the opening force required to open the valve externally.
StoneCold:
Horizontal, 2-inch taps the 8-inch on top, rises vertical, about a 4-foot horiz. of 2-inch w/ a 2-inch air release on top :No check in the 2-inch bypass.
This is a domestic water distribution system, about 7K feet of down steam 8 & 6 inch and 25 houses, no storage. The idea is to force low flows through the 2-inch and add chlorine based on flow (in the 2-inch), high flows open the check and go on w/o extra chlorine.
Thanks
Steve
P/S additional comments welcomed!