Compressors not up to it ?

[W.olly]

Well after hours yesterday faffing to set this up and get the pressures set, i think. I dont think the two compressors are upto the job.

So as i `think` the settings are ok and the set up ok i hope you guys can confirm eithe right or wrong please.

The set up is

Both tanks Max psi 150psi.

Comp 1 Airmaster 15/60 3hp 50l 14CFM (?)
Comp 2 Jetair J11 50l 3hp 11CFM

Comp 1 Cut in 95psi/ Out 125psi
Comp 2 Cut in 80psi / Out 130psi

Reg set at 90psi


Now with the valve on the discharge Nozzle set a half open and a little less it works fine with a third turn of abrasive valve being turned.

All i get though is about 6 sq inch done before Comp 1 kicks in, then a minute after Comp 2.

Then they both need to run constant to keep the pressure up, it does not drop or get higher.

When i stop blasting Tank one cuts out then a minute or so after Comp 2 cuts outs.


The lines are white 3m 8mm bore to a Y piece with filter then reg, and then yellow 10m 10mm bore to the blast tam filter.

You think it is upto the job. dont want to burn anything out. Ihave been usingn 30m extension lead fully unwound and the cable get warm. Will use two separate leads next time i think.

 

[rtbcomp]

My two worked exactly the same. They say a compressor should run at a 50% duty cycle (15 mins on, 15 off) but I haven't had any problems with a 20 gall pot.

 

[gaz1]

another tank on those will just make them run longer before cutoff point once you use the extra air they will just keep pumping air into the tank

id have used 10mm done all the lines

with that you would still only get 9" done instead of 6

a 22cfm has to pump just as much air into the tank as the tools do drain them quickly in some cases with prelonged use you have to wait for pressure to rebuild back up again

i have used a 100litre tank and that gets warm after a while and the system still needs to refil back up before use again continuos use and it drains it badly as ive found out

 

[optima21]

you could always use a smaller nozzle in the blasting gun to use less air if you want the compressors to switch on and off

 

[rcx132]

Haven't others said they've run these pots of a single garage compressor? I think low cost compressors are over rated, they don't do anywhere near the CFM that they claim.

Not sure compressors have a duty cycle. The garage ones can run at 100% as they have cooling and the DIY compressors will cut out when they get too hot.

 

[W.olly]

another tank on those will just make them run longer before cutoff point once you use the extra air they will just keep pumping air into the tank

id have used 10mm done all the lines

with that you would still only get 9" done instead of 6

a 22cfm has to pump just as much air into the tank as the tools do drain them quickly in some cases with prelonged use you have to wait for pressure to rebuild back up again

i have used a 100litre tank and that gets warm after a while and the system still needs to refil back up before use again continuos use and it drains it badly as ive found out

I am only using one tank, the second is shut off so not being filled.

you could always use a smaller nozzle in the blasting gun to use less air if you want the compressors to switch on and off

Bloody nora,i bet thats it, well could help and after the faff about i forgot to check that.

Just checked the size and i can get a 3.5mm drill bit in with a slight bit of play so could be 3.75mm as a 4mm will not fit.



Thanks for the help guys

 

[rcx132]

Someone also said that those pits are fine at 60 psi.

 

[brightspark]

I buy a 3mm or a 2.5mm carbide jet and cut the contraption of the end and fit new carbide jet in using jubilee clip and operate from input shut off tap .it takes a 80cfm compressor to run a 6mm jet at 90 psi so half that and it gives u an idea . I also run a 3mm jet on another pot I have at 28cfm 90psi continuous

 

[optima21]

this might help with nozzle size and air requirement.

http://www.blastitclean.co.uk/page6a.html

 

[rcx132]

buy a 3mm or a 2.5mm carbide jet and cut the contraption of the end and fit new carbide jet in using jubilee clip and operate from input shut off tap .it takes a 80cfm compressor to run a 6mm jet so half that and it gives u an idea

A 6mm jet has 112 sq.mm. a 3mm jet has 28 sq.mm. So if a 6mm jet need 80 CFM then a 3mm jet needs 20 CFM.

 

[W.olly]

I am using 0,5mm~ abrasive so if i get a smaller tip like a 2.5mm it should be best to get a longer run before the comp kicks in then.

Its hard to say though if i am getting the CFM from the two Compressors which should be around 25CFM.

Tell you what this tech talk on the CFM and psi needed is over my weee brain here.

I wills ee how it goes with a 2.5mm tip. Keep the settings as they are and go from there.


And if i did run as it is and the two compressors running all the time to keep the pressure up how long should i run before i give them a rest ?

 

[rcx132]

Everything has a duty cycle.

Including you.

Let's say you can comfortably run for 10 minutes. Then, to do another 10 minutes (at the same intensity) you need to rest for 30 minutes. You have a 25% duty cycle with a 40 minute baseline.

If you exceed your duty cycle you feel bad.

Letting a machine (compressor, welder, soldering iron, whatever) go so far as shutting down due to thermal protection is like you running flat out until you get cramp, throw up and pass out (in any order). The difference is that you have a self repair mechanism to cope with damage.

Oh, and by the way, DIY compressors have cooling too.

Equipment usually states it's duty cycle but I couldn't find one for the compressors hence my conclusion.

The thermal cut out on DIY compressors could be set to cut when the compressor is tired (using you analogy) and not necessarily when it's cramped out, removing the necessity to state a duty cycle.

 

[rcx132]

And if i did run as it is and the two compressors running all the time to keep the pressure up how long should i run before i give them a rest ?

That's what we are arguing about. The duty cycle tells you how much they need to rest but I don't think compressors state a duty cycle which made me think they can run continuously. I don't like them running continuously, it feels wrong, but lots of equipment is designed to.

 

[rtbcomp]

A 6mm jet has 112 sq.mm. a 3mm jet has 28 sq.mm. So if a 6mm jet need 80 CFM then a 3mm jet needs 20 CFM.

That may apply to pure air, don't forget there is media mixed in with the air which effectively reduces the cross-sectional area of the nozzle.

6mm diameter = 3mm radius, area = pi*r*r = pi*3*3 = pi*9 = 28.27 sq.mm

3mm diameter = 1.5mm radius, area = pi*r*r = pi*1.5*1.5 = pi*2.25 = 7.06 sq.mm

Although the ratio is still 4:1, ie the square of the diameters

...

And if i did run as it is and the two compressors running all the time to keep the pressure up how long should i run before i give them a rest ?

I would say rest for F minutes every R minutes, where F is the time it takes to refill the pot and R is how long it will run on a pot-full of media. You could extend the rest period by however long it takes to drink a cup of coffee.

 

[rtbcomp]

I am only using one tank, the second is shut off so not being filled.

....

I think Gaz meant receiver rather than pot?

 

[rcx132]

That may apply to pure air, don't forget there is media mixed in with the air which effectively reduces the cross-sectional area of the nozzle.

6mm diameter = 3mm radius, area = pi*r*r = pi*3*3 = pi*9 = 28.27 sq.mm

3mm diameter = 1.5mm radius, area = pi*r*r = pi*1.5*1.5 = pi*2.25 = 7.06 sq.mm

Although the ratio is still 4:1, ie the square of the diameters

You did spot I used diameter instead of radius, an error.

I might phone Sealey to ask about duty cycle for my compressor.

 

[brightspark]

depends on how far u want to kane your pump. I run one of mine as long as it takes to complete the blasting and yes it gets hot

 

[brightspark]

I have a 14cfm pump that will run 24 /7 on a 3 hp motor its an air brake compressor of a wagon

 

[dannyp]

direct drive compressors melt but belt drive i've ru my clarke continus and for the first hour i pointed the ir thermomiter at it, it was hot but stabel so i left it to it

 

[rcx132]

I've got direct contact with Sealeys head of workshop, as my compressor is a Sealey, I've just emailed him to ask about duty cycle.

I wouldn't be surprised if they can run continuous, lots of equipment does, many central heating pumps run all winter non-stop, cargo ships run non stop for days..

Happy to accept that I shouldn't be straining my DIY compressors, but then what's the alternative if you've only got single phase. I've got a 3HP/14CFM garage compressor and two DIY compressors and they don't keep up with mask+HVLP gun, or air hungry air tools like needle scalers or MBX tool. The DIY compressors are totally over rated, they claim 9.5 CFM but only have a fraction of the output of the 14CFM garage compressor.

My Sealey compressor claims 10CFM free air delivery, and my mask claims 10 CFM consumption. If I connect the two the compressor pressure guage doesn't move, it doesn't go down, but also doesn't climb, so Sealeys claimed output is about right. If I do the same with the DIY compressors, which claim 6.5 CFM free air, and hook up up to a 4 CFM die grinder, what happens? After 2 minutes the compressor is dead. Whats really surprising is the power they use, the garage compressor measures 13A consumption. The DIY compressors draw 10A, so they are totally inefficient as well.

Last night I looked at cost of a high CFM pump and 5 - 10 HP motor to make a compressor that can run off a 32A plug, and it's still serious cost £800 for pump + £400 motor. 14 CFM pumps are much cheaper, £150, so was thinking to keep the 14CFM/3HP garage compressor and make a second 14CFM/3HP rig. And ditch the DIY compressors.

And when people calculate their CFM needs they are forgetting to account for wear and tear. An older compressor will be doing less than it's new counterpart.