Steam Reduction

[finite]

What is the maximum pressure differential that could be used for acurate control through a steam control valve. The pipe diameter on the inlet is 2 inch?

 

[TD2K]

Retaining control is a matter of the valve opening rather than simply the dP. If the valve gets too far open or too far closed, you lose the ability to control the process be it pressure, flow, whatever. Granted, high dP leads to high outlet velocities and that can create other issues (noise, vibration) but those aren't directly 'control' issues (or not as I consider them).

Generally, for sizing, you don't like to go much under 20% or over 70% open on the control valve. In operation, I tend to push that to 10% to 80% or 85%.

 

[abeltio]

An old rule of thumb says that you can use up to a 25%~30% of the total pressure drop in the system in the control valve (this in turn should give you enough dp at the valve to have the valve around 60~70% open @ design conditions
E.g. the total system pressure drop @ design point is 45psid (exclusive of the control valve), so the max pressure drop in the valve can be estimated as:
total dp = valve dp + 45psid
total dp = 0.25 total dp + 45psid
total dp = 45psid/(1 - 0.25)
total dp = 60 psid
valve dp = 0.25 total dp
valve dp = 15 psid

This is a very simplistic approach that applies to most liquids (liquids like : water, gas-oil, oil) where you can achieve turbulent flow (Re > 2000).
If you have compressible and/or multi-phase fluids the situation may be different as other considerations may apply (critical vs. sub-critical flow).
Slurries are a different story too...
Hope this helps.
a.