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spray gun question


I just bought a C.A. Technologies HVLP spray gun that came with a reduced pressure air cap. When and why would i want to use the reduced pressure air cap. I have always owned HVLP gravity spray guns but never had one with a reduced pressure air cap.
The manual says i can use tip sizes of .08 to 2.2 with the HVLP cap and .08 to 1.7 with the reduced pressure cap.


3/5/20       #2: spray gun question ...

Maybe to limit bounce back, in corners, inside boxes, door details ?

3/5/20       #3: spray gun question ...

I believe reduce pressure air cap is so that it will comply with laws in some jurisdiction
It also allows better transfer without too much overspray

3/5/20       #4: spray gun question ...
DannyB Member

The RP cap has much better atomization, and is compliant with the 65% transfer efficiency rule.
But it is not HVLP.

For jurisdictions that require *HVLP* you cannot use it.
For others that only require compliance to the transfer efficiency requirement, and don't dictate the method, you can use it.

The advantages: Better atomization, lower CFM requirement, wider fan pattern/speed of spray.

The disadvantages: Lower in-practice transfer efficiency than HVLP.

3/5/20       #5: spray gun question ...

Thanks for all of your answers.
DannyB what do you mean." Lower in-practice transfer efficiency than HVLP"


3/5/20       #6: spray gun question ...
Daniel Berlin

I mean lots of people can get 75-85%+ transfer efficiency out of an HVLP cap with good technique.

That is a lot less likely from an RP cap.
It is a harder, faster spray.

(I have a bunch of CA Tech guns, including the CAT-X and CPR)

3/5/20       #7: spray gun question ...

Danny is spot on.

Old school high pressure(auto) 30% transfer easiest to use.

New school high transfer 65%
decent to use, material savings alone makes sense, labeled HVLP on guns but doesn’t satisfy some jurisdictions.

Accuspray’s been doing real HVLP 80-90% transfer since the 1990’s. Many other brands since the 2000’s.

3/5/20       #8: spray gun question ...

Hey DannyB
Do you normally use the HVLP cap or the RP?


3/6/20       #9: spray gun question ...
Daniel Berlin

I usually use the RP.

Mainly because i'm lazy and willing to deal with the material wastage.
i don't have anywhere near the volume some folks here do. If material cost was a huge factor, i'd reconsider.

I also spray a wide variety of stuff (urethanes, CV's, etc).

With water based coatings and the HVLP cap, i find i have to be significantly more careful with technique and setup to avoid issues (microbubbles, etc).

I do actually have a dedicated HVLP gun set up perfectly for some of the high cost 2k urethane product i spray.

If i was spraying one product and one kind of thing consistently (or maybe one kind of clear and one kind of pigment), i'd probably just dial in settings perfectly and go with HVLP cap, and leave it alone.

3/14/20       #10: spray gun question ...
Jim Conklin  Member


We have been using CAT pressure fed guns for years. Mostly in the "Feline" line as in FEFF or finish excellence(they have some weird naming schemes).

By naming confusion I bought a CPR-FE that came with the reduced pressure aircap. We all love it for lacquer and conversion varnish clears. The HVLP cap goes unused. Weirdly, the RP cap yields what we think is a finer atomization. With a bit more overspray - kind of like an HTE gun. The cap orifices are certainly smaller. Both the HVLP and the RP cap call for 29 psi inlet pressure.

When we get on the HVLP FEFF gun, we are like "Whoa, the line pressure is too low, look at those huge droplets." Usually the finish is fine regardless, but the difference out of the gun is noticeable.

If the CoronaVirus doesn't kill me, I'm gonna try the CAT-Xpress on our topcoat pot, move the CPR-FE to the sealer pot and the FE-FF to the pigment pot.

3/15/20       #11: spray gun question ...

Hi Jim
Thanks for the response. I used the RR cap last week to spray some cabinets and book shelfs. Some had some pretty big backs that needed sprayed. It was the first time i ever used an RP cap and i really liked it. It seemed to me that 29 psi was to high. I was spraying Sherwin Williams high build pigmented lacquer at 20 psi. Next time i use it i will try it at 29 psi.


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