PRINCIPLE OF OPERATION
The SkoFlo valve is a pressure
independent flow control valve used in
the petroleum industry to accurately injec
chemicals. The valve consists of a body,
ase plate that is bolted to the body, and a
flow rate adjustment handle.
The principle of operation of the Model
SF15000NMF SkoFlo valve is that it
internally maintains a constant differential
pressure across an adjustable Cv section,
thus resulting in a constant flow through
that Cv section. The piston/spring
assembly utilizes system pressure to
adjust the internal pin and seat Cv section
which then sets a constant differential
pressure across the adjustable Cv section,
thus maintaining a constant flow. Flow
rate changes through the valve can only
be made by adjusting the rate adjustment
handle.
Fluid enters the valve inlet at pressure P
1and flows into chamber 1. It then flows through the
adjustable Cv section into chamber 2 where the piston and springs are located. These springs
put a force against the piston based on how much the springs are deflected. The spring force
against the piston is set by the differential pressure between P
1in chamber 3 and P2in chamber
2. This pressure balance establishes the pressure P
2in chamber 2 at a fixed differential from P
1.
Flow then exits the valve at pressure P
3after passing through the seat. The flow through the
seat is held back by the pin that mates with the seat. As the pressure in chamber 2 changes,
either as a result of a change in P
1or a change in P3, the pin moves in relation to the seat and
controls pressure P2. As soon as equilibrium flow through the valve is established, the flow rate
will remain constant even when pressures upstream and/or downstream of the valve change.
Rate
Adjustment
Handle
Adjustable
Cv Section
P
1
P
3
P
2
IN
OUT
CHAMBER 2
P
2
CHAMBER 3
P
1
CHAMBER 1
P
1
Springs
Pin
Seat
Piston
Valve
r:\msoffice\excel\e-mail\o_manuals\SkoFlo sf15000nmfa\sf15000nmfa-manual-a1 Page 3 of 13
