The 25P is a self-actuated pilotoperated pressure regulator. Downstream pressure is fed back through an external sensing line to the pressure pilot, which adjusts the opening of the main valve so as to maintain the set pressure. The valve meets Class IV shut-off specifications but is not suitable for dead-end service.
The Spirax Sarco FTI contains a float valve mechanism which modulates to discharge condensate continuously at steam temperature while non-condensible gases are released by a separate internal balanced pressure thermostatic air vent. The in-line piping connections simplify installation.