Steam Traps: The important link between good steam and condensate management

Steam Traps: The important link between good steam and condensate management

by PROS April 25, 2023

Steam Traps in the Cleaning Industry

Written by Barry Victor, Founder of PROS Parts

Steam heated devices are used in many applications in laundry and dry cleaning plants.  Steam can be used in finned heat exchangers to heat air for drying of textiles in laundry dryers and dry cleaning machines.  It is also used to heat the cylinders in flatwork ironers or other types of finishing equipment and it can be used to boil solvent in the distillation process in dry cleaning machines.

As steam provides the energy to heat the processes, it is converted to condensate or liquid water.  The device that controls the removal of the condensate is called a steam trap. Ensuring your steam traps are in good working condition saves energy and time.

The purpose of a steam trap in any pressurized steam heating system is to control the discharge of air and water from the system without permitting the exit of live steam before it has expended its heating potential.  As steam circulates through a heat exchanger, heating the media on the other side of the heat exchanger wall, it changes state from a gas (steam) into a liquid (water).  If a steam trap is incorrectly sized, the wrong type, improperly installed or malfunctioning, it can dramatically reduce the ability of the heat exchanger to supply the necessary steam for the heating task or waste the heat potential of the live steam which would increase the energy cost of the process.

There are typically two types of steam traps used in the cleaning industry, inverted bucket and thermodynamic.  Each type has its strengths and weaknesses and should be applied in the proper situation.  There are many manufacturers of steam traps.  PROS offers Spirax-Sarco, Armstrong, Gestra and United Brass.

Inverted Bucket Trap

In the startup position as shown below, the inverted bucket is in the down position causing the arm to open the valve to the trap condensate outlet.  Condensate enters the bucket and flows down and around it towards the valve and to the condensate outlet.  If steam enters the bucket, it will rise causing the lever to close the valve.  The valve remains closed until the steam condenses or passes through the vent in the top of the bucket into the top of the trap area.  As the bucket sinks, the lever causes the valve to open and allows the accumulated condensate to discharge.


If air reaches the trap, it will accumulate in the bucket and cause it to rise and close the valve.  The valve remains closed until the air bubbles through the vent hole at the top of the bucket.  Due to the small size of the vent hole and the small differential in pressure, the trap is relatively slow at passing air.  This can be overcome by adding a parallel air vent line outside the trap.

Inverted bucket traps are best suited for relatively steady pressure and load conditions, making them very suitable for laundry and dry cleaning equipment.

Thermodynamic Trap

Thermodynamic steam traps operate on a simple principal based on the dynamics of water and flash steam. It has only one moving part which is a disc that operates against a seat.  On startup the incoming pressure raises the disc allowing the cool condensate and air to pass through the seat and exit the trap.  As hot condensate enters through the inlet passage into the chamber under the disc it releases flash steam moving at high velocity.  The high velocity creates a low pressure area under the disc which causes the disc to be drawn towards the seat.


The flash steam builds pressure in the upper part of the chamber forcing the disc down until it seats on the outlet ports.  At this stage of the cycle, the pressure above the disc is equal to the pressure below the disc. However because the surface area above the disc is greater, it is forced into the seated position preventing the flow of steam or condensate.   As the flash steam in the chamber above the disc condenses, the pressure falls and the pressure of the condensate under the disc causes the disc to raise and the cycle repeats.

PROS Parts is always here to help you with your steam trap needs! Visit our website for more information or you can always contact us directly.


About Barry Victor

Barry founded PROS Parts in the spring of 1988. Before starting PROS, Barry worked in the sales and engineering departments of Vic Manufacturing, one of the largest manufacturers of dry cleaning equipment in the U.S. At Vic, Barry launched a parts sales division that supported dry cleaning equipment imported from Italy and Germany. In its early years, PROS manufactured dry cleaning machinery and then evolved into an industrial and commercial laundry equipment and dry cleaning operations parts supplier. Barry lives in Eden Prairie, MN with his wife. He has two sons, a step son, a step daughter and his dog, Sora. 

Barry can be reached at 763-231-7379 or barryv@prosparts.com.

Inverted Bucket Trap diagrams from pipingengineer.org
Thermodynamic Trap diagrams from wermac.org


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