Odd behaviour?

[Davek0974]

Hi all,

My compressor is a new 8cfm unit with a 50ltr tank, has one regulator and twin outlets on it.

I just got a new air impact wrench and it needs 90psi max, so I thought I would drop the regulator on the pump to 90 but if set at 90 without air flowing, when I operate the wrench, it drops to about 40psi then goes back up when the flow stops. If i set 90 with air flowing it goes up to125 when flow stops.

Is it normal to have to adjust pressure regulators only when air is being drawn off or does this indicate a crap regulator or something else??

Btw the air line is 8mm rubber about 10m long.

We have larger air lines at work and the regulators stay the same whether air is flowing or not apart from a little drop at the instant flow starts.

Dave

 

[brightspark]

Hi all,

My compressor is a new 8cfm unit with a 50ltr tank, has one regulator and twin outlets on it.

I just got a new air impact wrench and it needs 90psi max, so I thought I would drop the regulator on the pump to 90 but if set at 90 without air flowing, when I operate the wrench, it drops to about 40psi then goes back up when the flow stops. If i set 90 with air flowing it goes up to125 when flow stops.

Is it normal to have to adjust pressure regulators only when air is being drawn off or does this indicate a crap regulator or something else??

Btw the air line is 8mm rubber about 10m long.

We have larger air lines at work and the regulators stay the same whether air is flowing or not apart from a little drop at the instant flow starts.

Dave

8mm bore is 2 small for air tools it needs to be min 10mm with minimum restriction . if u set the regulator to 90 psi it will drop in pressure a bit when in use. a decent half inch bsp filter reg will run at over 60cfm and wont restrict the flow. 15mm bore pipe would be better over 10m

 

[rtbcomp]

Is the reg on the compressor or at the end of the airline near your wrench?

If it's near the wrench then what BS says explains what's happening. If it's on the tank then it doesn't.

In the latter case it could be because the reg. can't handle the airflow, you'll need one with 1/2" BSP connections.

You'll still need the 10mm air hose as BS says though.

The best way to connect it up would be to have the hose connected directly to the tank and the reg. near to where you're working. That way the hose will be at tank pressure and so will overcome the resistance of the hose more easily.

 

[Davek0974]

The reg is on the tank, usual setup with tank gauge and line gauge etc, it reads to me like there is a restriction between the reg and tank, maybe a duff fitting or something blocking the flow a bit?

The reg fittings look very small, maybe 1/4"BSP at a guess, but it's only rated 8cfm and the wrench only needs 5cfm according to the booklet.

 

[rtbcomp]

They'll be 1/4. Is there a larger blanked-off port on the tank anywhere you could use?

I wouldn't pay too much attention to the CFM figures.

Most of the restriction will be in the regulator itself.

 

[brightspark]

The reg is on the tank, usual setup with tank gauge and line gauge etc, it reads to me like there is a restriction between the reg and tank, maybe a duff fitting or something blocking the flow a bit?

The reg fittings look very small, maybe 1/4"BSP at a guess, but it's only rated 8cfm and the wrench only needs 5cfm according to the booklet.

1/4will be useless 3/8th minimum and half inch more apropriate thats the problem

 

[Davek0974]

Ok, I'll look into it.

I think there is the usual bung in the domed end of the tank, I'll look into fitting onto that I reckon.

 

[rtbcomp]

That's what I did on my Clarke.

 

[Davek0974]

Ok, I've 'borrowed' a 1/2" regulator from work, I also got some reducers and adaptors, will have a go at fitting this weekend.

Had a quick look tonight and there is a 1/2 BSP bung in the end so thats good, looking at the other reg, it is fitted on the end of what looks like 1/4bsp pipe off of the tank then into a tee with the pressure switch, tank gauge and finally the filter /reg hopefully the bigger feed And much larger regulator will cure it.

 

[brightspark]

Ok, I've 'borrowed' a 1/2" regulator from work, I also got some reducers and adaptors, will have a go at fitting this weekend.

Had a quick look tonight and there is a 1/2 BSP bung in the end so thats good, looking at the other reg, it is fitted on the end of what looks like 1/4bsp pipe off of the tank then into a tee with the pressure switch, tank gauge and finally the filter /reg hopefully the bigger feed And much larger regulator will cure it.

in a nutshell yes

 

[octo0072000]

that's only a small 8 CFM on your compressor small tank as well you will find you are waiting about till it builds pressure up a lot of the time
1/2 impact gun uses 8CFM (Clarke one) all you can do is try it but a bigger tank and 150psi would be a lot better

 

[Davek0974]

Ok, all fitted up, I stripped the old regulator off, the passageways were tiny and rusted as there was no blasted pre filter! Took a line straight off the pressure switch outlet for the plasma cutter in 10mm flexi about 3 feet long, that seems very happy now as it has a built in filter regulator.

Then I fitted the bigger filter regulator to the 1/2" tank bung and then off that into a pcl coupling for my tools, all pipes are 8 or 10mm bore I know it's not ideal but that's what I have. The tools are much happier now, set reg at 90 and there is a small blip as air is drawn but now it quickly recovers to the set pressure as expected.

I am guessing the rusted up crappy regulator was the bottleneck in air flow so I can recommend anyone with a cheapy compressor to bin the reg and fit a proper one with a filter, it's worth it.

The air tools are rated 5cfm and the plasma was 6cfm so the pump can just about keep up when cutting, not ideal but tis is all shoestring setup as cash is tight as always, mostly use a blow gun for cleaning crap out of holes etc after machining them.

 

[rtbcomp]

Great stuff, thanks for letting us know the outcome!