Regulator Question - "PSIG Pressure Drop"?

[ElectroPulse]

Hello all,

I'm getting ready to purchase a replacement for the cheap regulator that came on my HF compressor, and I've been reading around and have seen the mention of "Pressure drop" on regulators. For example (https://www.grainger.com/product/WILKERSON-3-8-General-Purpose-Air-Regulator-6B212):
"For the Max. Flow, the CFM is measured with 100 psig inlet adjusted to a set pressure of 90 psig and a 15 psig pressure drop."

The way it's worded, it sounds like some standard method used when rating a regulator's CFM... I'm just having trouble figuring out what exactly this means? Just wanting to make sure it's that (and how exactly that works into their rating system), and not that the regulator eats 15PSI in some way (coming out of a 125PSI compressor, that'd be a bit much) (and no, I'd rather not run regulator-less).

Thanks!

 

[larry_g]

Anything in a plumbing system is going to cause pressure loss. Look up standard losses for pipe fittings. If you have something that is requiring near max flow of that regulator then you are going to have a pressure drop. At the flow rate most of us use you will see little to no loss.

lg
no neat sig line

 

[ddawg16]

As Larry noted above, anything in the system is going to have a pressure drop.

A regulator will always have some drop across it.

What you need to look at is the min pressure drop at the max flow you expect.

Or, look at this way. If you remove the regulator and and go just straight hose....the pressure at the tank is going to be greater than the pressure at the hose end. The pressure drop across the system is a function of flow, pressure, and line resistance.

 

[ElectroPulse]

Thank you for the replies!

So what is that number then? After reading your replies, and thinking about it, I'm thinking this is it:
-They measure PSI going into and coming out of regulator. They keep pulling higher and higher CFM until there's a 15PSI differential between input and output, and that's the CFM they rate it for.

Is that correct? And is this a standardized method of rating regulators across the industry?

 

[pancho400cid]

They measure PSI going into and coming out of regulator. They keep pulling higher and higher CFM until there's a 15PSI differential between input and output, and that's the CFM they rate it for.

That is exactly what they are saying. That is a lot of pressure drop. If your system actually runs around the 83 CFM ballpark a lot, I would say you need a bigger regulator with more flow capacity.... but that's a big compressor. If you have a typical 5 HP or less compressor your system wouldn't be drawing anywhere near that CFM. In other words - not good for a jackhammer. Probably OK for one-at-a-time shop air tools.

Do you have a separate filter? If not you should consider a filter/regulator combo.

A whole "nuther" question is whether they mean SCFM (standard cu. ft./min) or ACFM (actual cu. ft./min)...... I'm not going there, but it kinda matters in this case because the air is cooling off big time through the regulator at that much flow.

 

[ElectroPulse]

That is exactly what they are saying. That is a lot of pressure drop. If your system actually runs around the 83 CFM ballpark a lot, I would say you need a bigger regulator with more flow capacity.... but that's a big compressor. If you have a typical 5 HP or less compressor your system wouldn't be drawing anywhere near that CFM. In other words - not good for a jackhammer. Probably OK for one-at-a-time shop air tools.

Do you have a separate filter? If not you should consider a filter/regulator combo.

A whole "nuther" question is whether they mean SCFM (standard cu. ft./min) or ACFM (actual cu. ft./min)...... I'm not going there, but it kinda matters in this case because the air is cooling off big time through the regulator at that much flow.

I'll probably never go over 30CFM (based on what I've read, that's around the max CFM of my 1/2 HF Earthquake 1190ft/lb impact wrench). Due to the low PSI (125) of my compressor, I'm just wanting to optimize the air system to reduce pressure drop as much as possible, so that the usable (at full power) capacity of my tank is maximized (so rather than needing to crank it to like 115, be able to leave it at 100 and still get 90psi at my tool). I just know that the high-flow fittings I'm going to be getting allow 70-ish CFM, so am kind of using that as a baseline for what I'm aiming for the other components to be at.

Out of curiosity, is there a calculator out there to calculate PSI drop at a different CFM, given the specs on that page? I don't even know what that would be called. Or is it just linear? (so at 41.5CFM, 7.5PSI drop, for example)

As for an air filter, based on what I've read, for infrequent use it doesn't sound like they're super necessary. I honestly don't see myself using my air tools very frequently at the moment (just recently started wrenching on my own car, but have run into 3-4 bolts that required an impact to get off), so would rather save that money for a couple/few years down the line when I get a decent compressor (assuming a filter really is not that necessary for someone that may use it once or twice every few weeks... Or even less frequently). Currently just running the 125PSI 21 Gallon HF Oil compressor.

Note: I'm not looking to purchase a $50 regulator for my $150 compressor I just ran across one of those in used condition on eBay, saw that wording, and was curious about it.

 

[pancho400cid]

I'm not an expert. To really calculate the pressure drop through an orifice, regulator valve, etc. is very complicated because the expansion cooling at different flow rate and yada yada yada. It is not linear, but it does not really matter. The safe approach is to buy a regulator with a "max" flow rate much higher than the flow rate of your compressor because up near the max number when air is howling through them, they are not going to regulate pressure worth a damn.

In sweeping general terms, the pipe size is about as good an indicator as any. Maybe double checking the published max flow rate.

The reg you linked to has 3/8 NPT fittings.... pretty safe to assume the designers had light to medium use air tools, etc. used one at a time in mind, and it would likely work great for that as others said, with little or no noticeable pressure drop.

Since your tank pressure is low, you probably can have a tee or second connection and run the impact straight off the tank pressure without the regulator drop. See what the max rated pressure is for the impact before doing that.

I think the "max" flow of the filter-regulator I bought was "125 CFM" which is bout 10 times the flow rate of my compressor (which I plan to upgrade someday). It has 1/2" ports I think. It was probably overkill, but when I use a sander or paint gun, the pressure needle does not perceptibly move.... that thing is REGULATING....

 

[ElectroPulse]

I'm not an expert. To really calculate the pressure drop through an orifice, regulator valve, etc. is very complicated because the expansion cooling at different flow rate and yada yada yada. It is not linear, but it does not really matter. The safe approach is to buy a regulator with a "max" flow rate much higher than the flow rate of your compressor because up near the max number when air is howling through them, they are not going to regulate pressure worth a damn.

In sweeping general terms, the pipe size is about as good an indicator as any. Maybe double checking the published max flow rate.

The reg you linked to has 3/8 NPT fittings.... pretty safe to assume the designers had light to medium use air tools, etc. used one at a time in mind, and it would likely work great for that as others said, with little or no noticeable pressure drop.

Since your tank pressure is low, you probably can have a tee or second connection and run the impact straight off the tank pressure without the regulator drop. See what the max rated pressure is for the impact before doing that.

I think the "max" flow of the filter-regulator I bought was "125 CFM" which is bout 10 times the flow rate of my compressor (which I plan to upgrade someday). It has 1/2" ports I think. It was probably overkill, but when I use a sander or paint gun, the pressure needle does not perceptibly move.... that thing is REGULATING....

I'm curious... How do you find the max flow rate of a compressor? You're meaning air leaving the tank, not how quickly it can refill, correct?

 

[larry_g]

Out of curiosity, is there a calculator out there to calculate PSI drop at a different CFM, given the specs on that page? I don't even know what that would be called. Or is it just linear? (so at 41.5CFM, 7.5PSI drop, for example)

There are charts for that regulator here, http://www.wilkersoncorp.com/brochure/Catalog605_08 18 28 Series.pdf . Check out pages 14-16. A lot of pneumatic components will give you a Cv number and from that you can mathematically figure the pressure drop. Most major manufactures will also have technical help on their web site to give you this information. Also notice that this regulator comes with 3 different port sizes yet all 3 have similar charastics, so port size is not a good indicator of flow capabilities.

In your situation I would run most things at full tank pressure and only add in a regulator if you need to run at some reduced pressure. Your rattle gun is not going to blow up with 125 psi supplied to it.

lg
no neat sig line

lg
no neat sig line