Required hold times for low-pressure air testing of gravity sewer and vacuum testing of manholes, with a countdown timer. Runs entirely offline; inputs persist in this browser via localStorage.
Safety — read before pressurizing anything: Compressed air in a plugged pipe stores real energy; plug blowouts have killed people. Brace or restrain all plugs against the thrust, never position anyone in a manhole or in line with a plug while the line is pressurized, relieve pressure before touching plugs, and read the gauge from grade. Air testing is a no-entry operation, full stop.
Which table governs: The times below are computed from the widely used UNI-B-6 / ASTM F1417 time formula (pipe) and the commonly published ASTM C1244 table (manholes). Standards get revised and specs sometimes adopt modified tables — where your contract documents include a test table, that table governs over this tool.
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Set the timer from a calculated hold time above.
How the Numbers Are Derived
Air test hold time formula
The UNI-B-6 / ASTM F1417 time for a 1.0 psig drop, based on an allowable air loss of 0.0015 cfm per square foot of internal pipe surface:
T = 0.085 · D · K / Q seconds, where K = 0.000419 · D · L (but not less than 1.0) and Q = 0.0015
with D in inches and L in feet. For K = 1 (short/small sections) this reduces to T = 56.7 · D seconds — the familiar "minimum time" column (e.g. 7 min 34 s for 8-in. pipe at 1.0 psig). Beyond the threshold length L = 2387/D ft, time grows with D²·L. Times for the 0.5 psig drop method are exactly half.
Groundwater adjustment
Groundwater above the pipe pushes back against the escaping air, so all gauge pressures are raised by the equivalent head: 0.433 psi per foot of average groundwater height above the pipe crown. The tool adjusts the pressurization, start, and fail pressures accordingly. When the required adjusted test pressure approaches 9 psig, air testing is generally not advised (plug thrust and safety) — dewater, or test by another method (low-pressure exfiltration, CCTV plus joint testing per the spec).
Vacuum test table
ASTM C1244 tests the assembled manhole (including joints and boots, lift holes plugged) at 10 in. Hg of vacuum; the manhole passes if the vacuum takes at least the tabulated time to drop to 9 in. Hg. Times scale with manhole volume — larger diameter and deeper barrels get longer times. The tool reproduces the commonly published table (8–30 ft depth, 30–72 in. diameter), rounds intermediate depths up to the next row, and linearly extrapolates beyond 30 ft with a warning.
Field notes
Let the air section stabilize at least 2 minutes (air temperature equalizing with the pipe wall causes pressure wander that looks like a leak). Bleed back down to the start pressure before timing.
Wet the pipe interior on a hot day if the spec allows — a hot dry pipe absorbing moisture from compressed air can fail a section that is actually tight.
A section that holds better than required passes early: the test is over as soon as the hold time elapses with less than the allowable drop.
For the vacuum test, a manhole that fails usually leaks at the chimney/frame joint, a boot, or an unplugged lift hole — soap the suspects before condemning the barrel.
References
ASTM F1417 — Standard Practice for Installation Acceptance of Plastic Non-pressure Sewer Lines Using Low-Pressure Air. https://www.astm.org/
Uni-Bell UNI-B-6 — Recommended Practice for Low-Pressure Air Testing of Installed Sewer Pipe. https://www.uni-bell.org/
ASTM C828 (clay) and C924 (concrete) — companion low-pressure air test methods.
ASTM C1244 — Standard Test Method for Concrete Sewer Manholes by the Negative Air Pressure (Vacuum) Test.