Steam traps can create major problems with your steam system resulting in reduced output, energy losses, downtime, and major maintenance headaches.

Steam traps fail for the following reasons:

1. Improper sizing.

2. Improper selection for an application.

3. Age and pressure.

4. Piping errors.

Sizing a steam trap is based on the condensate load to the trap, pressure differential across the trap and safety factor.

Three quick formulas can be used to calculate the steam load for many applications.

Heating water with steam

Q = GPM/2 x (temp rise)

Heating air with steam

Q = CFM/800 x (temp rise)

Heating oils with steam

Q = GPM/4 x (temp rise)


Q= lb/hr of steam

GPM= gallons/ minute

CFM=cubic feet/minute

The pressure differential across the trap is inlet pressure minus outlet pressure. Trap inlet pressure is line pressure to the trap less any pressure drop through control valves and equipment. Trap outlet pressure is the combination of static pressure plus any pressure due to elevation changes. For most applications, use a safety factor of twice the actual load.

Selection of trap type is very important to achieving success. All steam traps are either blast or modulating in operation. Blast traps are two position devices; either open or closed. Modulating traps function like a level control and adjust their discharge rate to match the steam consumption in the equipment.

All bucket, thermodynamic (disc), and balanced pressure thermostatic steam traps are blast traps. All float and thermostatic traps are modulating traps. All applications where the steam to the equipment is controlled should use a modulating trap. All constant pressure applications can use a blast trap.

Age and pressure affect steam trap life. The higher the operating pressure, the shorter the service life. Blast traps generally have shorter service life than modulating traps due to the nature of their internal operation. At 100 psig, expect service life for bucket, thermodynamic, and the older lever arm style float and thermostatic traps of 3-5 years on average.

If the average service life in your plant for traps is five years, then statistically you can expect 20% of the traps to fail each year. A single 1/2" trap will waste $ 10,000 per year. Checking and replacing steam traps yields very fast paybacks and better system operation.

Piping errors result in premature trap failure. All steam traps should be installed with a discharge check valve, inlet and outlet isolation valves, and inlet strainer. Always allow condensate to flow to the trap and lift from the trap. Make all return lines at least equal in size to the trap connections.

Attempting to lift condensate on equipment applications where the steam supply is controlled will lead to flooding and trap problems. By definition, a control valve will adjust to what ever position is required to maintain your set point. In many cases the valve will either be throttled close to a closed position or closed. If the back pressure is equal to or greater than the inlet pressure to the trap, no flow can occur resulting in flooded equipment. On applications of this type, use a condensate pump.

Steam traps should be checked two times per year. Use a combination of temperature profile and sound to look for proper trap operation. Test equipment to check traps can be purchased for less than ,500 and will quickly pay back in fuel savings.

Got a steam trap question? Give us a call.