Pressure — Reading It, Converting It, Testing It. Episode eighty-three of the Gas Service Animated series.

Pressure has three jobs on a gas call: you read it to diagnose, you convert it to speak both dialects of the trade, and you test with it to prove a system tight. Three jobs, three procedures, and one instrument at the center — the manometer. This is the pressure episode the other sixty were leaning on.

The conversion spine: one p s i equals twenty-seven point seven inches of water column. Residential delivery runs about seven inches — a quarter of a p s i. A two p s i elevated system is fifty-five point four inches. And the old ounce gauges: sixteen ounces to the p s i, so seven inches of water is about four ounces. Same low-pressure world, three dials describing it.

Before any table cell means anything, match its pressure family. The sizing tables come in drop families: table 6.2.1(a) spends three-tenths of an inch, (b) spends half an inch, (d) spends six inches, and the two p s i tables spend a full p s i. Same pipe, different budgets, wildly different capacities. Reading a cell from the wrong family is fiction with confidence.

Reading procedure, inlet side. Gas off. Crack the eighth-inch inlet tap on the gas valve — or tee at the drip. Zero the manometer first, every time; a gauge that starts at a lie only tells lies. Connect, restore gas, appliance still off — and that number is static pressure: the system at rest, around seven inches on a healthy street.

Now make it work for a living. Fire the appliance at full input — and put the other big loads on too, because worst case is the only honest case. That reading is dynamic pressure. Healthy looks like a small dip — six point eight static to six point two firing. Starved looks like a sag below the appliance's listed minimum, commonly around four and a half to five for natural gas. Then bracket it: repeat at the meter. Low everywhere is supply-side; a sag only at the appliance is the piping in between.

The third tap is the manifold — the gas valve's outlet, burners firing. Set it to the nameplate: typically three and a half inches natural gas, ten to eleven propane — the manufacturer's number, always. Adjust at the regulator screw, then prove the change with a combustion check. Manifold pressure is a setting, not a diagnosis.

Job three: the section 8.1 pressure test — new, repaired, or added piping, before it ever carries gas. The medium: air, nitrogen, or inert gas — never oxygen. The pressure: at least one and a half times working pressure, and never less than three p s i. The hold: ten minutes minimum for a single-family system. The gauge: full scale no more than five times the test — a three p s i test on a hundred p s i gauge cannot see its own leak. And the appliances: anything rated below test pressure is disconnected and capped, not just valved.

Pass or fail is binary: any unexplained pressure drop is a leak. Locate it with a listed detector or noncorrosive fluid — never a flame — repair, and retest from the top. And keep the two worlds straight: the three p s i test proves new pipe with inert gas; the everyday check when gas is restored is the section 8.2.3 leak check at operating pressure. Different pressures, different purposes, both mandatory in their lane.

Pressure in one breath. Twenty-seven seven to the p s i. Match the table's drop family. Zero, then static, then dynamic under full fire — the sag tells you where. Manifold to the nameplate, proven by combustion. New pipe: three p s i minimum, right-sized gauge, appliances capped, any drop is a leak, retest after repair. Restore gas, leak check at operating pressure. Next: the vent tables, decoded.