Seventy-four seconds. That was the number on a cold storage dock's inspector's test last winter, and the building owner's first question was whether the valve was broken. It wasn't. The system was big, nobody had ever written down a previous time, and so nobody knew if 74 was bad or just normal for that riser.
That's most of what a dry pipe trip test is. Not the trip itself, the comparison.
Two tests that sound like one
The annual test is a partial flow trip. You open the inspector's test or the main drain on the system side, let the air bleed down, and the valve trips. Water comes into the system piping up to the clapper and you check that everything behaved. You do this in warm weather, because a valve full of water in a freezing building is its own callback.
The three year test is the full flow one. Same trip, but you actually push water out the inspector's test connection and time how long it takes to arrive. That's where the 60 second number lives.
Quick version of the difference:
| Annual | Every 3 years | |
|---|---|---|
| Trip the valve | Yes | Yes |
| Water out the end of the system | Not required to the far end | Yes, at the inspector's test |
| Time delivery | Record trip pressure and behavior | Record seconds to water |
| Season | Warm weather | Warm weather |
| Reset and re-prime after | Yes | Yes |
Check your AHJ and the edition they enforce. I've seen the three year test folded into the annual one when the contractor just wants one trip a year instead of two, and nobody objected. Still, write on the report which one you ran.
The 60 second thing
Sixty seconds is the number most people quote for water to reach the test connection from the moment the inspector's test opens. It comes out of the design side, and it has exceptions (small systems, systems with a quick opening device, certain hazard setups). So don't treat it as a universal pass or fail. Look at what the system was designed and accepted for.
Here's a log from a mid-size warehouse system I'd call typical, anonymized:
| Year | Trip pressure (psi) | Air before (psi) | Seconds to water | Notes |
|---|---|---|---|---|
| Original acceptance | 26 | 40 | 38 | Baseline |
| Year 3 | 25 | 40 | 41 | Fine |
| Year 6 | 26 | 40 | 47 | Slow, checked low point drains |
| Year 9 | 26 | 40 | 62 | Found partially closed section valve |
Nothing in that table says "failed" until year 9, but anybody holding last time's number would have been asking questions by year 6. The jump from 47 to 62 was a valve somebody had cracked closed after a repair. That's an impairment, by the way. If you find that kind of thing, the impairment procedure kicks in.
Air pressure and priming water
Boring, and it's where most dry systems actually get into trouble.
Air pressure: the system should sit at whatever the valve manufacturer calls for, usually somewhere in the range of 15 to 20 psi above the valve's trip point. Too close and a little air loss trips the valve on a Tuesday night. Too high and you slow the water down. Log it before you do anything else.
Air loss: if you're topping off all the time, you have a leak. I've used 1.5 psi a week as the number where I start looking, but confirm against the edition your AHJ uses. Dont quote me on that one for every jurisdiction.
Priming water: every dry valve has a priming level, usually just above the clapper seat or at a marked sight glass. Too little and the seat can leak air. Too much and you get a mess. The manufacturer's sheet will tell you the exact level, so keep it in the job folder.
When the valve won't reset
Happens more than people admit. In rough order of what I check:
- Was the system fully drained? Water sitting at a low point (no drum drip emptied, a trapped section) will hold the clapper on its seat the wrong way.
- Is the seat clean? Grit or a bit of pipe scale from the trip is the classic culprit.
- Did the clapper latch? Some valves need a specific reset sequence, and it's different between brands.
- Is the air supply actually keeping up, or is the compressor or maintenance device the real problem?
If the clapper is chewed up or the seat is scored, stop. Replace the part. Do not fight it and leave the system in service hoping it holds. Tag it, notify the owner, and follow your impairment steps while you wait for parts.
What goes on the report
Trip pressure, air pressure before and after, seconds to water on the three year, priming level, anything you found at the low points, and a signature. Put last time's number right next to this time's. That one habit would have saved me and that cold storage owner an afternoon. If you want the bigger calendar around this, the NFPA 25 inspection schedule lays out where the trip test sits against the rest of the year.
Digging last year's seconds-to-water out of some old scanned folder is the part that wore me out, and it's a big reason I built FireDeck (free right now while I'm still testing it).
Anyway. Write the number down.