Air regulator question.

Darren · Apr 25, 2007

Periodically I mount 24" truck tires. The number usually varies from 40 to 60. Most times the tires are "aired up" at night for safety reasons. I've found that using a regulator on the air line slows things up. It seems to take forever to get to 90 psi. On the other hand by eliminating the regulator, the pressure ends up around 120 psi in much less time if I'm not constantly checking. FWIW, the tires are rated for 120.

I like using a regulator because I don't have to waste time releasing air to get down to 90 psi and I can work another tire once the rings seat, but it means I'm lucky to get 5 tires done an hour when I get can more done without the regulator.

The question: is there a way to use a regulator and speed up the time to get to 90 psi. A larger compressor is not an option.

638 · Apr 25, 2007

This question came up 30 years ago when I was employed at the brewery. We used air bags as dunnage in the railroad cars to keep cases of beer from moving around during shipment. I was assigned the task of comming up with a method of inflating the bags rapidly to a pressure of 4 lbs. With a regulater in the line it took forever to inflate but did not over inflate. I was never able to come up with a practical solution to the problem.

ron

schmism · Apr 26, 2007

how about a custom pop-off valve.

in theory you could tune it to 120psi. so you run regulator less, to 120psi it pops off, bleads off 5 or 10psi and resets and starts filling again. when it pops off you go attend to it, top off the tire check pressure and move on.

Farmerford · Apr 26, 2007

Schism is right. McMaster Carr sells ASME rated air popoff valves preset in 5 psi increments for $10 or so. I use one set at 115psi for filling a portable air tank that is rated below the main air supply pressure. I stay in the shop where the compressor is located and disconnect the air chuck when I hear the valve pop.

AlanB · Apr 26, 2007

Or just a regulator with a larger flow.

I like the pop off valve idea though.

Not sure what a water heater pop off valve is set too, but that may be a cheap option readilly available at Lowes etc. I think they are adjustable as well.

638 · Apr 26, 2007

The problem is, that due to the restriction in the valve stem itself, the air presure in the line to the valve stem will be at the regulated pressure and the pop off will 'pop off'. Let's think about this for awhile. Perhaps with an adjustable restriction before the popoff valve (after the regulator), and an air pressure gauge at the pop off valve, the air flow could be adjusted to a balanced point that would not pop off until the desired tire pressure has been reached. I think that it would be worth a try.

ron

Farmerford · Apr 26, 2007

That does not happen with me to any great extent. The pop off valve is in the branch of a pipe tee that has the clamp on air chuck in one run and a male quick connect in the other. I connect the chuck to the tank first and then connect the air line to the tee. Since the portable tank is usually empty the air flows pretty fast at first. Maybe the long air hose (100' of 3/8" ID) and the tee provide enough restriction to keep the pressure at the tee below the pop off pressure until the portable tank is nearly at the pop off pressure. The pop off valve is only a few inches from the portable tank (albeit the valve stem that is part of the path is quite restrictive), but it is 100' from the compressor, and the air flows through several 1/4" pipe fittings and a hose reel to get to the portable tank. The compressor is only 3hp with a 20 gallon tank, so once it comes on it runs continuously until the portable tank is disconnected. In my case, the portable tank is rated for 125 psi and the main source is 140 psi. And you are right that the pop off valve does open before the tank gets to the pop off pressure, but it is only a few psi before. As the portable tank pressure approaches the supply pressure the rate of flow declines and therefore the pressure drop through the supply path lessens, and the pressure at the pop off valve gets closer to the supply pressure. If Darren has the problem you mention he could put a ball valve between the tee and the quick connect for the supply line to regulate the flow.

Tom_Veatch · Apr 26, 2007

The only thing that affects the pressure drop between the the relief valve and the plenum (i.e., tire or portable air tank) is the air flow rate and the flow resistance/restrictions in the line between the valve and the plenum.

The higher the flow rate - you want that as large as possible - the greater the pressure difference will be between the plenum and the relief valve when the valve pops - you want that as small as possible. You can minimize that pressure difference by minimizing the flow resistance downstream of the relief valve. There isn't much you can do about the restriction of the plenum's fill valve, but you can minimize the pressure drop by keeping the line/hose between the relief valve and the plenum as short, straight, smooth, and large a diameter as possible with no more fittings than are absolutely necessary.

638 · Apr 26, 2007

OK, how about this. Use mutiple hoses, say, fill 6 tires at a time. Change a tire, start filling. Change another tire, start filling. By the time the 6th tire is changed and started to fill, the first tire should be up to pressure, etc.

ron