While I was making some midnight rounds on a start-up, I found an operator draining a large amount of condensate from a waterlogged exchanger to grade.Ball Valves He asked why it was taking so long. The exchanger had a float trap lined up to the condensate system but no check valve, so the condensate was merely backflowing from the condensate return system. Resilient Seated Gate ValvesI have previously noticed that it is generally not recognized by operators (and some engineers) that most float traps do not have an integral check valve- if there is level in the trap, liquid flow can pass either direction depending on the pressure.Butterfly Valves

At another company I worked at it was standard detail to include a check valve after the float trap. This is also shown in the Spirax-sarco hook-ups manual. The standard drawings at this site for exchanger drain traps does not include a check valve.

Does any best practices for exchanger process trap drain piping? Are there any special start-up or loss of steam hazards that can exist because having (or not having) a check valve?Bellows Seal Valves

It sounds like you need a condensate pump because if you have higher pressure in the condensate line than at the inlet to the steam trap.  Typical heat exchanger 'stall'.
Yes, a check valve will prevent back flow, however, you still will not be able to drain your condensate due to lack of differential pressure.Check Valves
Many systems with modulating control valves cannot handle ANY backpressure, and may even run under a vacuum, even with positive pressure entering the heat exchanger.  This problem is often solved by isolating the heat exchanger from the rest of the condensate system - using a pump.

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