Ball valves to replace gate v wprovided with minimum flow stop to prevent full closure"

[VIAR97]

Hi
I'm working for ball valve manufacturer.
we have been requested for MOV ball valves in lieu of gate valves, requested previously, but with the following mandatory requirements:
- inching facility on electric actuator
- valve provided with minimum flow stop to prevent full closure
the process service is well fluid to production manifold and valves will be used for intermittent service. valve failure position: stayput.

my main concern, apart from the request of inching facility on motor, is this requirement about minimum flow stop to prevent full closure

can anyone explain this request and most of all if this can be performed by a ball valve (on/off) without damaging seats?

Thanks in advance.

 

[gerhardl]

Regarding electric actuators, any movement can be programmed on modern top-grade actuators. Limitations will be on speed combined with necessary force and available EX- versions if relevant.

Damage of seals are depending on closure degree and pressure difference across the minimum opening, eg abrasive factors and turbulent versus laminar flow.

Shell-type V-port ballvalves (in exotic materials, ceramic version or steel in descending degree) can in degrees within different limits handle this, but not always.

If the 'leaking' requirement is rather small, an extra boring through the shell (away from the v-opening) could possibly give the desired flow, with the valve v-port in closed position. But only if the demand for leakage is permanent and no permanent closing is necessary over the v-port valves.