On new low/medium pressure installations, put a bleed valve on the condensate line inside the block valve.
This way if there is a question about a trap, the operator can block in the condensate return, open the trap outlet to atmosphere, and watch it thru several cycles.
The best method of detection depends on the type of trap and the pressure/temperature of the steam system. The best way to detect operation is definitely through physical testing. Physical testing normally requires a Tee with a hand valve be installed between a steam trap and an isolation valve. This allows you to isolate the trap from the condensate system and to vent the trap to atmosphere during operation so that the cycling of the trap can be observed. Some manufacturers offer steam traps with built-in test manifold assemblies. If the steam is high temp/pressure, physical testing may not be safe or practical. Through personal experience, I have found that ultrasonic testing is the next best method for traps that operate in a cyclic manner. For continous operation traps, such as Float & Thermostatic traps (F&T traps), discerning a leaking trap from a well operating trap can be challenging. On critical operation, some F&T traps have connections for a sight glass; under operation, the sight glass should never be empty and you should see the level fluctuate with operation. I am not a fan of infrared temperature measurements (thermography and thermometers) to find leaking or failed open traps - I have done comparative testing and have found that only extreme gross leakage can be detected using infrared testing, if it detects the failure at all. Thermal testing equipment can range from $20,000 for a state of the art infrared camera to $200 for an infrared "gun" thermometer. It is however a very good method to find failed closed traps. For me, I have found combining ultrasonic testing with immediate upstream and downstream pipe temperature readings to be the most effective way of detecting a trap failure (both open and closed). No matter which method you use, training and consistency are the keys to proper diagnosis. There are various ultrasonic testing systems on the market that have traps signatures stored in internal memory to remove subjective judgement from the testing process. The signature of the trap tested is compared to the internal signature of a properly operating trap (of the same type) to determine pass/fail. Personally I prefer a well trained technician.
