Trying to understand air line pressure drop

[md21722]

Trying to understand and eliminate pressure drop, I took some measurements. All tests were run with a 1HP angle grinder 35-37 SCFM. I have a 60 gallon tank with about 8-10' of 1/2" hose going into a 1/2" black iron pipe manifold that also gets a 1/2" feed from another compressor & a 3/8" feed from a smaller tank compressor. This then feeds into a Milton 1108 filter and regulator combo. The Milton filter (the brass sintered type) and regulator are rated 250 PSI 100 SCFM. I also took a T-fitting and put couplers on each end and a gauge on the third port so I can measure pressure as close to the tool as possible.

With 1/2" NPT fittings & hose ends:

Test 1. Using 1/2" big body Milton G style fittings and the angle grinder (has a 3/8" NPT big body G style fitting) plugged directly into the regulator I show 12 psi drop (108 psi static pressure gives me 94 psi running pressure just before the tool).

Test 2. Same as #1 except I used a 1/2" air hose, 25' length. 1/2" NPT ends. I measured 18 psi drop

With 1/4" NPT fittings & hose ends, 3/8" hose:

Test 3. Same as #1 except using Milton V style fittings 16 psi drop.

Test 4. Same as #2 except I used a 3/8" air hose, 25' length. 1/4" NPT ends. Milton V style. 26 psi drop.



Is 12 psi drop across the filter and regulator normal?

The losses across the hose seem OK.

 

[Wes J]

There is no way to eliminate pressure loss in any kind of piping system. All you can do is reduce the number of bends, Ts, and other transition. Increasing pipe size also helps.

Look up "K factors". They are published coefficients of pressure loss for most kinds of fittings and types of tube and pipe.

 

[CNGsaves]

Put in real Airline System. Take out that gobbly gook. Short 3 ft hydraulic hose that is 3/4" at Tractor Supply that connects compressor to airline system. Keep entire airline system at 1/2" or larger. Mainline of 3/4" and drops of 1/2" would be good for your situation along with Loop for airline system around shop. Black pipe steel or copper for airline system.

Don't need regulator for straight grinding which is air hog. Crank up pressure on compressor, and keep airline system at same psi. Put regulators at drops ONLY where you need lower pressure.

 

[md21722]

Put in real Airline System. Take out that gobbly gook. Short 3 ft hydraulic hose that is 3/4" at Tractor Supply that connects compressor to airline system. Keep entire airline system at 1/2" or larger. Mainline of 3/4" and drops of 1/2" would be good for your situation along with Loop for airline system around shop. Black pipe steel or copper for airline system.

Don't need regulator for straight grinding which is air hog. Crank up pressure on compressor, and keep airline system at same psi. Put regulators at drops ONLY where you need lower pressure.

This is my home "shop" which is part of the space I'm renting so I'm mindful about "permanent" improvements. The only 3/8" feed is from the small 2HP contractor compressor for extra air. The 60 gallon has a straight shot into the regulator. For these tests I had the valves for the others closed off. With or without the other tanks there is no change in the pressure drop. As I understand it, 1/2" hose will flow about 100 SCFM. I consider the filter mandatory to keep junk and water out of my tools. I have not separated the filter from the regulator.

Is your suggestion to replace the 1/2" hose with a 3/4" feed into the regulator?

I agree in a perfect world I would have a 3/4 - 1" air line in a loop with 1/2 - 3/4 drops.

 

[larry_g]

With unimpeded flow you have to drop all the pressure some where. I assume that you are just letting the tool run at WOT with no load. Put a load in the tool and see what happens. Without load there is no restriction to flow and with no restriction to flow you will not build pressure. Are you having problems with your grinder getting the job done?

lg
no neat sig line

 

[CNGsaves]

^ ^ ^ Sorry didn't know this was "rental" space so not permanent. Yes I would still go with 3/4" hydraulic hose (3 ft) as your flexible attachment to what ever airline system you put together. You can use that later when you move to a permanent place.

That initial 8 to 10 ft of 1/2" hose right after compressor is worst thing you can do to cool down air and capture water. It is doing opposite by restricting flow and building up water. Rubber hose is terrible material for airline system.

To assist you in peak air demands (ie heavy CFM air grinder), why not put that extra compressor at END of airline system so you'll have extra storage vessel and capacity ?? This would also give you dryer air from the main compressor since it has time to cool in airline system.

For your airline system, I'd just scab together bits and pieces of 3/4" black pipe steel as makeshift mainline. At end, bring a 1/2" drop UP and then back down to feed your air needs of grinder. Airline system should have downward slope to drain any water into a "dump drop" that has ball valve at end of line. Your T to add that extra compressor would be just before that last drop, or even T'd into that last drop.

If you end up with more that 20 ft of black pipe steel, likely need NO filter/regulator on that whole stretch from compressor. A filter/regulator could be on the extra compressor on end to manage pressure and capture any water as it doesn't have length of airline system to cool down the air.

Keep your airline system at HIGH pressure . . . .same as main compressor shutoff.

Good luck.

 

[md21722]

^ ^ ^ Sorry didn't know this was "rental" space so not permanent. Yes I would still go with 3/4" hydraulic hose (3 ft) as your flexible attachment to what ever airline system you put together. You can use that later when you move to a permanent place.

That initial 8 to 10 ft of 1/2" hose right after compressor is worst thing you can do to cool down air and capture water. It is doing opposite by restricting flow and building up water. Rubber hose is terrible material for airline system.

To assist you in peak air demands (ie heavy CFM air grinder), why not put that extra compressor at END of airline system so you'll have extra storage vessel and capacity ?? This would also give you dryer air from the main compressor since it has time to cool in airline system.

For your airline system, I'd just scab together bits and pieces of 3/4" black pipe steel as makeshift mainline. At end, bring a 1/2" drop UP and then back down so that slope of line will drain any water into a "dump" drop that has ball valve. Your T to add that extra compressor would be just before that last drop.

If you end up with more that 20 ft of black pipe steel, likely need NO filter/regulator on that whole stretch from compressor. A filter/regulator could be on the extra compressor on end to manage pressure and capture any water as it doesn't have length of airline system to cool down the air.

Keep your airline system at HIGH pressure . . . .same as main compressor shutoff.

Good luck.

Well maybe I should've discussed my air compressors LOL. The 8-10' 1/2" line comes off a 60 gallon tank that has a low volume dual stage compressor. It puts out a whopping 4-5 CFM (measured) and the tank itself is super thick 3/16" shell and heads and doesn't really get hot. The head of the compressor never measures more than 150-175F. The other two are single stage and run 25-40 feet of rubber hose before they get to the filter/regulator. Those do get higher temperatures with their cylinder heads measuring around 300-325F. For the purpose of these tests, the compressors were not running as I was just running it for a few seconds to measure pressure drop.

I'm sure under load the angle grinder uses less air. Depending on conditions, I can grind for over 20 minutes straight and not run out of air and I only have 19 SCFM. I used the angle grinder as an experiment because both my ratchet & impact use the same amount of air. And the angle grinder has a 3/8" NPT inlet whereas the ratchet & impact have 1/4" NPT. With the 3/8" NPT it seemed easier to use the big body Milton G style fittings.

I am thinking of running a loop around the garage anyway. I am thinking some wood screws through the drywall with unistrut and pipe clamps. Then I can just fill in the wholes when I leave. My current project is to upgrade the compressor system with a Champion R15.

I suppose a more accurate test is to measure pressure drop under load as larry_g suggested.

 

[TigerDude]

The regulator should only have a pressure drop if it's set to.

We could figure out actual pressure drops, but offhand, it seems to me that 1/2" pipe seems small for that high a cfm.

 

[larry_g]

The regulator should only have a pressure drop if it's set to.

Your wrong with this statement. All parts of the piping system will have pressure drop. With all the orifices, diaphragms, curves and filter medium the FR subjects the air flow to they are commonly a fair restriction to flow.

lg
no neat sig line

 

[md21722]

I looked up some performance charts and it looks like every regulator Parker sells has a decent pressure drop across it. It took me a bit to find a manufacturer that provided this information.

 

[ovrrdrive]

I always just adjust the pressure at the tank regulator until I get the target psi at the end of the hose I'm using while the tool is engaged. Just turn it up until you get the pressure you need and don't worry about it.

I have what I consider to be a pretty well flowing system and to get 90psi at the end of the hose I need to run it around 120-125 out of the tank.

 

[pcmeiners]

"I looked up some performance charts and it looks like every regulator Parker sells has a decent pressure drop across it."

Parker does have some nice info on it's air devices, I would not say Parker has decent pressure drops across all their regulators. If you look at all their regulators, if you go with expensive, large ported regulators,like >3/4", more like 1", there is very little loss.
Basically, throughout your entire system you will have significant loss unless your entire system is oversized. On my system nothing is under 1", all filters, regulators have minuscule losses. With piping you want to minimize Ts , short radius elbows, standard valves (get full flow valves) , under engineered check valves (high loss device). If users insist on purchasing 1/4"-1/2" (or even some 3/4" ported devices) you are going to have significant losses; if you not willing to pay, you get what you pay for .

 

[ddawg16]

It's simple......if you have flow, you have pressure drop.

As an example, think of the hoops designers go through designing intake manifolds.

So, the smaller the line, the higher the velocity to get the same CFM. If you want more CFM with the same line, increase pressure.

You can have a 12" dia line feeding your 3/8" hose....but it will only flow what that 3/8" will allow.

 

[md21722]

What I did is scrap my old system and buy 2, 5HP dual stage air compressors. The compressors cut on at 135 and cut off at 175. I can drop 60 psi before my big tools start getting less than 90 psi running.

The old system, with two larger single stage compressors, didn't have nearly as wide a band. The compressors came on at 105 and shut off at 130 so the tool was already seeing only 80 psi by the time they came on.

 

[md21722]

"I looked up some performance charts and it looks like every regulator Parker sells has a decent pressure drop across it."

Parker does have some nice info on it's air devices, I would not say Parker has decent pressure drops across all their regulators. If you look at all their regulators, if you go with expensive, large ported regulators,like >3/4", more like 1", there is very little loss.
Basically, throughout your entire system you will have significant loss unless your entire system is oversized. On my system nothing is under 1", all filters, regulators have minuscule losses. With piping you want to minimize Ts , short radius elbows, standard valves (get full flow valves) , under engineered check valves (high loss device). If users insist on purchasing 1/4"-1/2" (or even some 3/4" ported devices) you are going to have significant losses; if you not willing to pay, you get what you pay for .

What is minuscule? Looking at the charts, I may save about 7 psi using 3/4" or 1" inlets (5 psi drop across the regulator, rather than 12, at 35-40 SCFM). At the cost of around an extra $100 per regulator? This is based on the charts I'm looking at. Not sure of real world hands on experience.

 

[sberry]

This is normal and not worth fussing with. You don't need 3/4 line either.