Throttling service, Temperature changes, Over-pressurization – Flowserve 50165 Nordstrom Figure User Manual
Page 6
Nordstrom Figure 50165 and 50169 Dynamic Balance Iron Plug Valve FCD NVENIM2006-00 – 09/05
6
Throttling Service
Valves used to control the rate of fluid flow may be subject to severe fluid turbulence that can have the
effect of creating a high-energy conversion within the valve and piping system. This energy conversion
is usually indicated by high noise levels, either from cavitation of liquids or shock waves from gases.
(The noise in a water faucet is an example of a low-level cavitation noise.)
The possibility exists for mechanical damage to the valve and piping system when throttling of liquid
flow results in severe and continuous cavitation conditions. Likewise, with gas flow under severe throt-
tling conditions, shock waves can possibly result in damage to the system.
Flowserve Nordstrom Valves should be consulted on proper valve selection for throttling applications.
Temperature Changes
Valve structural materials expand with rising temperatures and contract with falling temperatures.
Generally, increasing temperature causes a decrease of mechanical strength that is regained on return
to a lower temperature. A condition of non-uniform temperature in a structure may impose significant
thermal stresses or distortion with possible adverse effect on valve performance.
The possibility of thermal stress fatigue should be considered in applications involving frequent
temperature cycling. This possibility is increased by any one or a combination of the following:
increasing temperature range, increasing temperature level, increasing rate of temperature change,
increasing thermal conductivity of the fluid, increasing thickness of metal sections or increasing the
number of cycles. In some cases, thermal cycling may also increase the tendency for stem seal leakage.
Over-pressurization
Dynamic Balanced iron plug valves are not provided with a pressure relief device. It is the user’s
responsibility to provide a relief device as part of the system in which the valve will be used.