Velan Design - Velan Piston & Bimetallic
FAST WARM UP
Cool air and condensate from the system is discharged through the large
main valve orifice actuated by the piston, which is held open by it’s
own weight when cold. As line pressure builds up pressure above the piston
keeps the valve open at maximum discharge until the system is completely purged
of air and condensate.
POSITIVE TRAPPING
Incoming steam contacting the bimetal element closes the pilot valve, thereby
reducing the pressure acting on the piston. Line pressure below the main valve
closes it tightly but smoothly, due to the partial pressure remaining in the
piston chamber.
CONDENSATE DISCHARGE
When condensate and air collect in the trap body, the bimetal force is reduced,
line pressure opens the pilot valve, pressurizing the piston chamber and forcing
the main valve open against line pressure by virtue of the greater piston
area.
CHECK VALVE ACTION
Excess back pressure, a drop in line pressure, or discharging to overhead
return lines, can cause a reverse flow of condensate through the trap. Normally
separate check valves are required to prevent this occurrence. The Velan type
SP main discharge valve also works as a temporary piston check valve and prevents
back flow.