Steam trap survey

A steam trap is a valve with one job

A steam trap sits at the low point of a steam system and does one thing: let condensate and air out, and hold live steam in. When it works, it is invisible. When it fails it does so in one of two directions — stuck open, blowing live steam straight to the return, or stuck closed, backing condensate up into the equipment it is supposed to drain. The first wastes energy by the thousands of dollars a year; the second floods heat exchangers, kills output, and sets up water hammer that can split a pipe. A survey is how you find both before they cost you.

The trouble is you cannot tell a good trap from a bad one by looking. A blowing trap and a healthy one both sit there hissing faintly. The whole survey is four checks that, read together, name the condition every time: inlet temperature, outlet temperature, an ultrasonic listen, and a look at the discharge. No single one is enough — it is the pattern across all four that tells you what the trap is doing.

The four checks, and what each one means

• Inlet temperature tells you whether steam is even reaching the trap. Hot inlet (steam temperature for the line pressure — about 338 °F on a 100 psig main) means the trap has something to work on. A cold inlet means nothing is getting there — the strainer ahead of it is plugged.
• Outlet temperature is the single most useful reading. A healthy trap discharges condensate, so its outlet runs well below steam temperature. An outlet nearly as hot as the inlet means live steam is passing straight through — a blow-through.
• Ultrasound hears what the trap is doing. A healthy trap makes an intermittent cycle — open, dump, snap shut. A continuous rush is steam blowing through; a rapid machine-gun chatter is a trap cycling itself to death; dead silence is a trap doing nothing at all.
• The sight glass shows the discharge directly — clear condensate on a good trap, a steam blow on a failed-open one, a flooded glass on one that cannot keep up.

The two that fool everyone

Two pairs of faults look identical until you read the one number that separates them, and both are on this trainer on purpose.

Failed-closed versus a plugged strainer. Both give you a cold, silent, dead trap with no discharge — and the reflex is to condemn the trap and cut it out. The inlet temperature is the whole diagnosis. A stuck-closed trap has a warm inlet: condensate is reaching it and stacking up against a shut valve. A starved trap — one whose upstream strainer has plugged — is cold on the inlet too, because nothing is getting through the strainer at all. Same cold trap, opposite fix: replace the trap in one case, blow down a strainer in the other. Read the inlet before you cut anything out.

Failed-open versus undersized. Both run hot and both flood the return or the process, and both get called "blowing." The outlet temperature separates them. A failed-open trap runs its outlet nearly as hot as the inlet — that is live steam. An undersized trap keeps its outlet at condensate temperature; it is passing condensate as fast as it can and still cannot keep up when the load peaks. One is a worn part to replace, the other is a sizing problem to redesign. The outlet reading tells you which.

Why the survey pays for itself

Studies of untended steam systems routinely find 15 to 30 percent of traps failed, most of them blowing steam — and a single blow-through trap on a 100 psig line can waste several thousand dollars of fuel a year, silently, forever, until someone reads its outlet temperature. A trap survey is one technician with a pyrometer and an ultrasonic gun walking the plant once a year. There is almost nothing else in maintenance with that return: the tools are cheap, the method is four readings per trap, and the pattern — hot in, cold out, cycling sound, clear glass — is the same at every trap in the plant. Learn to read it and you can survey a whole facility in a shift.