I'm adding a 35' run of 1" black pipe with 3 drops for a grill, gas log and backup generator to an existing 50' run of 1' pipe for a hot water heater and furnace. I'm trying to plan the pressure test at this time. My current plan is to test the whole system, of 5 units, by adding a pressure gage and valve to an existing 1" pipe drain. I'll then close all 5 unit valves, hook a compressor up to the added valve and pressure gage, and pressurize the system to 15 psi. My question is: this system under test will include the meter, since the only main shutoff valve is upstream of the meter - will this test harm the meter?

Hi Bob...

Great question! I'm glad you asked instead of finding out the hard way! The fact is that you CANNOT test through the meter... must remove the meter and cap off the outlet or you could install the test gauge here for the test.

Here, if you were to test through the meter, especially at 15PSI, it is very likely that the internal meter DIAPRAGHM would rupture and I promise you the gas company would know you busted it and charge you for the meter and the labor.

Technically, you're also supposed to disconnect all the appliances at the union fitting and cap the pipes. In other words, you're not supposed to just shut the shutoff at each appliance and then perform the test because a shutoff can fail and pressure can get by and could potentially damage the gas valve(s) at the appliances. AT 15 PSI I would remove the unions and cap the ljnes for the test.

All of this can be a pain but so can replacing a bad meter or a bad gas valve so I would recommend that you proceed as suggested, OK?

Mark

Mark,

Thanks so much for the assistance. I'll be sure to remove the meter and cap the appliances downstream of the valves when I run the pressure test.

Another question: I'm concluding that all systems leak at elevated pressures, it's just a matter of how much pressure and time. This suggests to me that these systems will also leak at low pressures, just less. Have you ever encountered a specification that says how much leackage is safe in a residential environment, in cfm? Thanks.

Bob

Hey Bob...

All systems leak at all pressures, eventually. However, that being said, if you did a good job putting everything together the pressure loss should not be too great within a 24 hour period.

And don't forget that with temperature change comes a pressure change. Here, as temp. increases so does pressure so you need to be aware of that as the day begins. Toward the end of the day, you could see a temperature drop and therefore a slight decrease in pressure, even if the pipes are tight, etc...

In my area we use a special gauge that reads in 1/10th PSI increments and we only use 3 LBS air pressure test for 15 minutes. Although that seems like a low pressure, that special gauge will find even the smallest leak in a system.

Anyway, no charts/specifications for pressure loss over time. Most residential tests are held for between 15 minutes and one hour so you should be able to hold the pressure as needed without any problems showing up at the gauge. If a problem presents then pump the system to higher pressure (remove gauge for this) and use a good SOAP solution and a spray bottle to soak the joints and find the leak(s).

Good luck!

Mark