Newbie - joining 3 compressors for sandblasting

[elitr6]

Hello all,

I've been dipping in and out of this great site for years but never registered.

I'm about to start a ground up restoration of a 1964 Land Rover 109SW, followed by my 1971 Triumph TR6. The Landys chassis and bulkhead need blasting back to bare metal, as does the TR6 body.

The high quotes and difficulty of transporting these items have convinced me to do the blasting myself.

I'm going to set up a temporary blasting/spraying booth on the patio behind the house. My dad's lending me a big plastic tent and I've got SWMBOs permission!

An 80L pressurised sandblasting pot should arrive shortly.

I've just bought two new identical belt driven compressors for the job. The specs are: 100L, 3hp, 230v, 240l/min output (8.4cfm). So I'll have a theoretical 480L/min together (16.8CFM). I've also got an older 2hp belt driven 100L that pumps out 190L/min (6.65CFM).

A friend is going to wire in 2 seperate 16A fuses and plugs and I'll run heavy duty extension cables (manual says 4mm2!) out to the patio.

I'm based out in the sticks in France so can only dream about popping into screwfix after work. Everything must be ordered on the net so I want to get the orders right first time around.

A few questions:

1) Is the tank outlet on most home/DIY compressors 1/2" BSPP?

2) I plan to install an elbow, ball valve then quick release socket on both compressors, all 1/2". Then a 1m hose to a 1/2" Y piece which would then feed into the regulator/filter with a quick release the other side. Does this sound ok?

3) Will the 2 new compressors suffice or should I also plumb in the 3rd one? It's going to cost a lot more in fittings

4) I notice lots of people have used copper pipe. As this is a temporary installation, would ID 10mm hose be ok?

5) I already have a filter/separator but it's 1/4". Would it be worthwhile upgrading to a 1/2" one?

6) Alternatively, and much more simply, I have to hand the fittings to link the 2 compressors from the quick releases after the regulators via a 1/4" Y piece and 10mm ID airline and into the 1/4" filter/regulator. It means no more spending but would it do the job? The compressors are equal sized so hopefully wouldn't damage the regulators.

Thank you!!!

 

[rtbcomp]

1) Don't know
2) Yes
3) Possibly, try it, if not plumb in the 3rd. Depends on nozzle size.
4) Yes
5) Yes
6) Some regulators don't like being back fed, take your air straight from the tank.

Make sure the compressors are set to switch on at slightly different pressures to avoid mains surges.

 

[elitr6]

1) Don't know
2) Yes
3) Possibly, try it, if not plumb in the 3rd. Depends on nozzle size.
4) Yes
5) Yes
6) Some regulators don't like being back fed, take your air straight from the tank.

Make sure the compressors are set to switch on at slightly different pressures to avoid mains surges.

Great, thanks! Looks like another 100quid to get all the fittings so I'm going to have to wait a bit before ordering everything

Would a 3mm nozzle make a huge difference over a 2.5mm when sandblasting?

 

[rtbcomp]

I think you'd notice the difference.

One thing that did strike me is that your compressors are rated at 3hp but only 8cfm, normally a 3hp compressor would deliver more like 14cfm. the difference is probably in the meaning of cfm.

I use a 3hp and a 2hp together with a very worn 2.5mm nozzle OK.

 

[elitr6]

I think you'd notice the difference.

One thing that did strike me is that your compressors are rated at 3hp but only 8cfm, normally a 3hp compressor would deliver more like 14cfm. the difference is probably in the meaning of cfm.

I use a 3hp and a 2hp together with a very worn 2.5mm nozzle OK.

Thanks. I've just taken the l/min output (FAD?) at 7bar and converted to CFM (10l/min = 0.35cfm)

 

[elitr6]

I found a mixture of water and gas fittings in a local shop. All for a lot less than I feared having looked online!

1/2" ball valve to stainless steel braided pipe (rated for 18bar/260psi - ID 13mm so 1/2") into 1/2" tee section (didn't have a Y) then 1/2" to 1/4" adaptor and into filter. Quick coupler on other side of filter.

The filter says mini-lubricator on it but looks like a filter to me. I'm not going mad, am I?

 

[rtbcomp]

Looks like a filter to me too.

 

[FranV8]

Rtb, there are two ratings typically quoted for a compressor, it's displacement, the higher one, flow of air if the swept volume were to 100% fill and discharge every stroke, and FAD, which is actual air delivery in normal circumstances.

I find for our sizes of reciprocating machines, allowing 3cfm FAD per hp seems a pretty good rule of thumb.

 

[rtbcomp]

I always thought FAD (Free Air Displacement) was the first one. How do you define "normal circumstances?" To give a volume delivery spec. you have to quote the pressure as the volume will decrease as the pressure increases for a given mass.

 

[elitr6]

Yup, the displacement on mine is 12cfm, so 24cfm together

 

[elitr6]

First try yesterday! I used 2 compressors (now with 1/2" regulator taking air straight from the tanks). There's a small annoying leak in the system and the nozzle cover/trigger has already worn down but other than that it works ok. I used a 3.5mm nozzle and had to let the system catch up quite often. I've just received a 3mm tungsten nozzle so will be fitting that this week.

Abrasive was Rugos 50/80

Also my first time using a paint gun!

 

[Shox Dr]

In the first picture there is still a lot of rust embedded in the pit holes. If you cannot be sure you have completely removed all traces of rust I would treat the bare metal with a rust neutraliser, just to be double sure. Other than that looks good

 

[rtbcomp]

Rust in pits is a devil to shift, you need to hold the hold the nozzle perpendicular to the surface and spend a bit of time at each point. When it looks OK you take your mask off and you see all the bits you missed!

 

[elitr6]

Thanks guys

I painted the axle with Bilt Hambers Electrox, which is very zinc rich. I hope it will keep the rust at bay!

 

[Shox Dr]

Zinc in paint acts as a barrier to UV light, slowing the break down. If you haven't removed all the rust it will not stop it getting worse. I say getting worse as it would be incorrect to say it comes back as you never got rid of it in the first place