ASAHI AV VALVES Installation,Operation and Maintenance Manual
Constant Flow Valves 4
(5) Principle & Operation
Refer to Figure 1 for design and operation of ASAHI AV
Flow Control Valve. When the upstream fluid pressure, P1
is introduced at the flow control orifice, it exerts a
corresponding pressure on the upper surface of the flange
on the piston type valve plug.
Likewise, the downstream pressure, P2exerts a
corresponding pressure to the lower surface of the valve
plug flange. Thus, when a differential pressure exists
between the fluid upstream and downstream of the orifice,
the corresponding pressure differential acting on the
surfaces of the flange moves the valve plug piston either
downward against the force of the spring cartridge or
upward by the force the spring, depending upon the
direction of the force induced by the existing pressure
differential.
This upward or downward movement of the valve plug
piston causes the flow orifice to be widened or narrowed
accordingly, thus the flow rate of the fluid passing across
the orifice is automatically adjusted.
For example, if the pressure differential, P1- P2 created between the upstream and downstream side of the
orifice increases, the valve plug piston moves downward to narrow the area of the orifice opening and
automatically adjusts the orifice to the preset flow rate value. (With the type of B, C and D, the plug has no
inlet hole for fluid, as the pressure differential P1- P2exerts directly on the surface of the plug.)
The reverse is also true when the pressure differential decreases, the piston moves upward increasing the
orifice opening area and allowing the fluid flow rate to increase to the preset value.
Preset flow rate range for use Design flow rate ranges:
Nom. size TYPE Flow rate (m3/hr) Rangeability Working differential pressure
TYPE B 0.04 - 0.8 20 : 1 0.02 - 0.1MPa (0.2 - 1.0kgf/㎝2)
15mm
(1/2”) TYPE C 0.08 - 0.8 10 : 1 0.03 - 0.2 MPa (0.3 - 2.0 kgf/㎝2)
TYPE B 0.06 - 1.2 20 : 1 0.02 - 0.1 MPa (0.2 - 1.0 kgf/㎝2)
20mm
(3/4”) TYPE C 0.12 - 1.2 10 : 1 0.03 - 0.2 MPa (0.3 - 2.0 kgf/㎝2)
TYPE A 0.5 - 2.0 4 : 1 0.02 - 0.1 MPa (0.2 - 1.0 kgf/㎝2)
TYPE B 0.1 - 2.0 20 : 1 0.02 - 0.1 MPa (0.2 - 1.0 kgf/㎝2)
25mm
(1”) TYPE C 0.2 - 2.0 10 : 1 0.03 - 0.2 MPa (0.3 - 2.0 kgf/㎝2)
TYPE A 2.0 - 8.0 4 : 1 0.02 - 0.1 MPa (0.2 - 1.0 kgf/㎝2)
TYPE B 0.4 - 8.0 20 : 1 0.02 - 0.1 MPa (0.2 - 1.0 kgf/㎝2)
50mm
(2”) TYPE C 0.8 - 8.0 10 : 1 0.03 - 0.2 MPa (0.3 - 2.0 kgf/㎝2)
TYPE A 5.0 - 20.0 4 : 1 0.02 - 0.1 MPa (0.2 - 1.0 kgf/㎝2)
TYPE B 1.0 - 20.0 20 : 1 0.02 - 0.1 MPa (0.2 - 1.0 kgf/㎝2)
TYPE C 2.0 - 20.0 10 : 1 0.03 - 0.2 MPa (0.3 - 2.0 kgf/㎝2)
80mm
(3”)
TYPE D 15.0 - 30.0 2 : 1 0.03 - 0.15 MPa (0.3 - 1.5 kgf/㎝2)
TYPE C 10.0 - 60.0 6 : 1 0.03 - 0.2 MPa (0.3 - 2.0 kgf/㎝2)
100mm
(4”) TYPE D 30.0 - 60.0 2 : 1 0.02 - 0.2 MPa (0.2 - 2.0 kgf/㎝2)
1m3/hr = 4.4033gal/min, 0.1MPa = 14.286PSI
Fig. 1
