Brochure

105F-27855-10
Cavitation Limitations on Valve Pressure Drop
A valve selected with too high a pressure drop can cause erosion of discs and/or wire drawing of the seat. In addition, cavitation can cause
noise, damage to the valve trim (and possibly the body), and choke the flow through the valve.
Do not exceed the maximum differential pressure (pressure drop) for the valve selected.
The following formula can be used on higher-temperature water systems, where cavitation could be a problem, to estimate the maximum allow-
able pressure drop across the valve:
Pm = 0.5 (P1 – Pv)
Where:
Pm = Maximum allowable pressure drop
P1 = Absolute inlet pressure (psia)
Pv = Absolute vapor pressure (psia)
Note: Add 14.7psi to the gauge supply pressure to obtain the absolute pressure value.
For example, if a valve is controlling 200°F water at an inlet pressure of 18psig, the maximum pressure drop allowable would be:
Pm = 0.5 [(18 + 14.7) – 11.53] = 10.6psi (Vapor pressure of 200°F water is 11.53psi.)
Therefore, if the pressure drop for this valve is less than 10.6psi, cavitation should not be a problem.
Systems where cavitation is shown to be a problem can sometimes be redesigned to provide lower inlet velocities. Valves having harder seat
materials should be furnished if inlet velocities cannot be lowered.
For additional valve sizing information, see the Vx-8xxx Selection Guide, F-27199.
Vapor Pressure of Water Table
Water
Temp.
(°F)
Vapor Pres-
sure (psia)
Water
Temp.
(°F)
Vapor Pres-
sure (psia)
Water
Temp.
(°F)
Vapor
Pressure
(psia)
Water
Temp.
(°F)
Vapor Pres-
sure (psia)
40 0.12 90 0.70 140 2.89 190 9.34
50 0.18 100 0.95 150 3.72 200 11.53
60 0.26 110 1.28 160 4.74 210 14.12
70 0.36 120 1.69 170 5.99 220 17.19
80 0.51 130 2.22 180 7.51 230 20.78
VB-82x3 Steam Capacity &
Vapor Pressures
5. VB-8/9000 Globe Valves
Sizing and Selection
5. VB-8/9000 Globe Valves
Sizing and Selection