Hi guys, new to forum and body work (last project was my '72 Firebird over 30 years ago). I'm not a professional but love tools and to tinker with all kinds of projects. I recently started digging into a small rust spot on my '05 F150 and it has morphed into a full scale repair. I'm planning to spray 2K Urethane primer (among others) that contains ISOs. After reading up on this decided I needed a supplied air respirator which brings me here...

So after reading up on these systems, I wound up getting a great deal on a new GAST 1023 pump off e-bay and decided to piece together my own Supplied Air Delivery system generally based off the Allegro A-750 system that looks like this



I sourced the same 50 micron intake filter, 0.5 micron HEPA exhaust filter, pressure gauge and pressure relief valve that is used on the Allegro system. However, I'm using stainless fittings throughout to build the manifold, a brass 3/8" body industrial interchange coupling, 3M 1/2" low pressure breathing hose and 3M respirators (both full face and half face, which I can change out based upon job).

Question is I believe the Allegro system uses a flow-through hose coupling on the pump, presumably to prevent the pump stressing if turned on without the airline and respirator connected. Of course, there is no need for this as long as the pump is not turned on without the respirator and airline connected. But I was thinking about drilling a 1/8" pressure bleed hole in the manifold just before the coupling just for safe keeping. I have a HVLP turbine paint system that has this same configuration.

Does anybody know if this pressure bleed hole would cause any problems with the respirator system or be sufficient to protect pump in the event it is turned on without the respirator being connected? I wouldn't think it would cause too much of a pressure drop or introduce a source for contamination to enter the system under use. Anybody have any experience with this?

Thanks in advance.

I think there is only one source that I would go to for this answer.... the manufacturer of the system. If this was just something that affected the performance of a gun, final coating, etc., that's one thing but here we are talking about your "life." Manufacturing firms like this have product liability that performs in relationship to their system designs. Honestly if they thought their "better mousetrap" needed a mod. like this for longevity, safety, performance, etc., it would be there.....

Thanks, yeah I get that. Problem is there is no manufacturer of this system as I'm putting it together myself. There are other systems that use the same pump and a closed coupling and they just say to make sure the airline and respirator is connected before turning pump on.

I am also using a pressure relief valve (PRV) so I suppose that would release if there was too much pressure. I tried looking up specs on the PRV that I'm using but can't find anything about what pressure it releases at. It is same model number used on the Allegro pump.

I guess I could try to find a flow through coupling for pump and hose. Probably overthinking this

Wow
All I can say is ....... Have fun with that There are a lot of systems on the Market now these days and I believe the ones that use a Turbine wheel system are far superior to any positive displacement pump design and in the end I can buy and use a whole lot of Carbon filters for my masks for years before I come close to the savings needed to purchase one of these fresh air systems.

To each His own, You wanna use that have fun dragging the hose and paying for it.
To the many others reading this there are alternatives.
And If it was Necessary the USA's EPA & OSHA would be all over it for workers in the USA.
Not saying that those agency's are inept or that the USA is behind the times but science just hasn't proven that the Carbon filter when taken care of properly and filters changed regularly are more than sufficient to handle the substances. Till they do I will be buying Carbon filters regularly and wearing my mask.

So you don't know if drilling a bleeding hole will impact performance, lol...

Anyway, yeah you can wear a cartridge type filter but (1) it should be the type that provides a vapor barrier, (2) it should be changed at frequent intervals, (3) filter cartridges can become saturated to the point where they no longer provide protection against ISOs and you can't tell by odor (4) once you've become sensitized to ISOs its permanent.

I'm not saying one approach is better than the other or even necessary.

Suggest anybody spraying ISOs read up on risks and make their own choice. One source of info is here http://multimedia.3m.com/mws/media/7778 ... Update.pdf

This is coming along pretty nicely. Just waiting for the intake filter. Company sent me wrong part but the right one is on the way. Tested it out this afternoon. Mask was comfortable. Airflow was strong and cool at the mask. Hose got pretty warm at the pump though. Overall happy with how it's coming out.

Intake filter arrived today...

OK don't shoot me down, be gentle.
So we breath around 7-9 litres of air per minute or 480 LPH. Why can't we use a fish tank/pond pump? Say we use a 1000 LPH one. Maybe it wouldn't have the ability to force enough pressure?