Direct acting PSV Mod. VSM
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When the valve reacts to modulate, in sustaining the upstream, pressure, the effective pressure
variation on the line depends on the length of the entire system and part of the network subject to the
VSM. This could take sometimes minutes, therefore allow for it before acting on the spring.
The flow rate is an effect of the pressure controlled by the VSM for that specific system. An inlet
pressure value, maintained for an instance at 3 bar, wouldn’t produce the same flow rate everywhere
as it depends on the headloss between the valve itself and the final boundary conditions.
Maintenance
The pressure relief/sustaining valve VSM is sturdy and reliable, and it was designed to minimize
maintenance. A semi-annual visual inspection for the proper movement of the piston and the
cleaning of the compensation chamber is recommended. A routine maintenance for gasket,
control, o-rings and if needed replacements is recommended every 4 years and explained on page
10 ref picture 1 on page 7. A possible malfunction can be identified by a leakage through the seat,
normally caused by dirt accumulated inside the body, or seeping through the shaft and leaking
through to the cover, hunting and excessive variation of the upstream pressure.
Set up
Before the start-up of the valve make sure the instructions provided on the maintenance
section “Installation” on page 5 were properly followed and understood.
Operate very slowly on the following procedure to avoid stresses on the valve and
unexpected pressure surges.
The valve is initially isolated from the main line by means of the sectioning devices
upstream and downstream.
Open the downstream gate valve by 30%, then open slowly the upstream sectioning device
to generate some flow through the valve. Make sure the maximum nominal pressure is not
exceeded during this operation.
Unless the valve has been ordered with a specific setting turn the adjusting screw (9)
anticlockwise to relief the spring (not completely), make sure VSM will respond with a
smooth modulation by reducing the upstream pressure increasing the flow.
Open completely the downstream gate valve.
Let VSM work and modulate according to the demand, act on the adjusting screw (9) by
turning it clockwise to increase the upstream pressure, anticlockwise to decrease and
check the pressure gauges for further reference.
Allow for enough time for the system to balance.
By means a pressure gauge upstream and a flow meter make sure that both the flow rate
and difference in pressure, in dynamic condition, don’t exceed the recommended values
displayed in the catalogue.
Be sure to allow for at least 5 mt increase in the set pressure occurring between dynamic
