Watson McDaniel Steam Design Guide

Float & Thermostatic Steam Traps Introduction

Thermostatic Air Vent (Open) when Air is present

A)Venting Air

A) When cold air enters the trap

during start-up, the thermostatic air vent is open, allowing the discharge of large quantities of air from the system.

Inlet

Air

Condensate

Steam

Outlet

Valve (Closed)

Thermostatic Air Vent (Closed) when Steam is present

B)Discharging Condensate

B) When condensate enters the trap, the float lifts which opens the valve, allowing condensate to discharge. This image shows the valve/seat fully open and operating at full capacity.

Elevated Condensate Level

Inlet

Outlet

Valve (Open)

C) Closed (Trapping Steam)

C) As the condensate discharges through the seat orifice, the float lowers, and shuts the valve. The float closes the valve with a level of condensate above the seating orifice to prevent loss of any steam. The float level rises and falls to modulate the seat opening in order to maintain a constant equilibrium between the incoming pressure and internal trap components, several orifice sizes are offered to accommodate various differential pressure ranges.

Thermostatic Air Vent (Closed) when Steam is present

Inlet

Condensate level always remains above valve seat to prevent loss of steam

Outlet

Valve (Closed)

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