Balanced Pressure Thermostatic Traps have a blast discharge with high air venting capacity. Their valve seat are wide open when cold.Operation: The trap is operated by a thermostatic fluid filled capsule. When steam is turned on, air discharges through the open valve orifice. Cold condensates enter passes out. At a temperature t below the saturated steam temperature corresponding to the pressure at the trap, the mixture boils exerts a vapour pressure. While the outside of the capsule is at steam pressure, the inside, because of the temperature head, is at a pressure higher by p . This excess pressure p closes the valve on its seat before steam temperature is reached. Condensate help in the trap, cools by t below steam temperature, until the vapour pressure in the capsule is below the steam pressure. The capsule contracts the valve opens. Since the curves of the fluid inside the capsule water are parallel, it does not matter what the steam pressure is in the trap. At any pressure p there will be an unbalanced force p holding the valve shut, after a temperature t below saturated steam temperature is reached. If superheat is present an internal pressure higher than p, is taken up by the flexible diaphragms in the capsule.Balanced Pressure Thermostatic Trap (BPT 21/AV 21) The BPT 21/AV 21 is a Thermostatic Steam Trap/Air Vent fitted with an inbuilt flat strainer screen having 0.8 mm diameter perforations. These traps are mainly used on Steam Tracing application. When installed at the end of steam line or process equipment, BPT traps functions as steam trap and when installed on steam line header, it acts as air vent.Thermostatic Instrument Tracer Steam Trap MST 21 The MST 21 steam trap is a maintainable balanced pressure trap designed for small condensate loads usually associated with instrument tracing applications. Manufactured in stainless steel it is corrosion resistant and is easily maintainable.Spirax Sarco' Bimetallic Steam Trap SM 45 The SM 45 is a medium pressure, temperature sensitive, maintainable steam trap. The operating element comprises a stack of bimetal discs which control the flow of condensate at a preset temperature below steam saturation.