Unusual paint sprayer question

[alex robinson]

I am hoping someone on here with knowledge of paint sprayers (and with a good imagination) may be able to help me with an odd request.

I work in a research lab. A colleague who works with microplastics has been suffering from RSI as a result of squeezing a squirty bottle too much when washing beakers and filters. (Cannot use tapwater - everything has to be multiple filtered etc and only pass through bottles / tubing made of glass, metal or PTFE).

We wondered if a paint sprayer linked to an air compressor might be a potentially more suitable way of doing this. Instead of multiple squeezing of the bottle, 1 gentle press on the trigger. A quick test with Screwfix's cheapest air compressor accessory kit suggests that it might be possible. However...

1) Is is possible / practical to get filters for the air supply. We would want a (preferably) glass fibre filter of around 20 microns.

2) What spray gun to get. We want almost the exact opposite of what people usually want. Instead of a fine even dispersion, we would want a relatively concentrated jet. Could this be achieved by blocking the side air nozzles? If would also need to have a very gentle to operate trigger. No idea if trigger pressure is something that people select paint sprayers for!

3) Could the hopper be attached to the side of the cabinet where the work was being done? Most gravity guns I have seen have the hopper fixed to the top of the gun, but I cannot see any reason why this couldn't be attached via a length of PTFE hose? Unlike spraying a car, there is no need to be able to move around.


The other option I have thought of is a peristaltic pump setup, but that feels like a more complex system that would need more building from scratch. Anything involving using air to pressurise a container of water is likely to have a long lag on the system, so cause a lot of dribbles.

Any thoughts or suggestions would be greatly appreciated!

 

[Jake]

What about a chemical type pressure sprayer, the sort with a handle you pressurise the container with - the expensive ones are stainless steel. Something like this

https://bestsprayers.co.uk/products/dual-stainless

 

[ChaiLatte]

2) What spray gun to get. We want almost the exact opposite of what people usually want. Instead of a fine even dispersion, we would want a relatively concentrated jet.

Every cheap set of compressor accessories comes with what is described as a paraffin spray gun. I think that meets the intent of what you describe in terms of jet.

It would appear to work on the principle you say you do not want (air entering and pressurising the vessel displaces the liquid) and would be made of unsuitable material but might give you some ideas.

Another place to look is Gloria sprayers - normally they are the pump up plant sprayer idea, but I think they offer a model that can be pressurised by an external supply (and has a built-in properly tested pressure relief valve so you do not accidently make a bomb. They offer a wide variety of nozzles as well as a wide range of non-metallic materials. They would probably make a custom nozzle for you if you could describe flow rate and pattern to them.

 

[Katomi woodsmith]

Have a word with your health and safety officer or HR
If the problem is explained see what they can do
Sorry to say this but my CYA (cover your backside) has just kicked in and I can see you personally being held responsible for bad practice / contaminated tests
And all the above as well as your work mate not being able to claim off the firm because you implemented a non approved method
If I am way out of line then
My most humble apploigies.

 

[ChaiLatte]

Could you assess what pressure and flow rate the standard squeezy bottle delivers?

It strikes me that a KISS system, of a gravity-fed spray head with a simple on-off valve could deliver similar performance. It all depends on if the available height will give enough pressure head. Put the tank on the roof and relocate the lab into the basement.

 

[alex robinson]

What about a chemical type pressure sprayer, the sort with a handle you pressurise the container with - the expensive ones are stainless steel. Something like this

https://bestsprayers.co.uk/products/dual-stainless

That could be an option. The hose will be a problem however. It will be a standard commonly used plastic so we would have to work out a way of switching it out for PTFE or fitting a 20 micron just before the nozzle. (Working with plastics is a pain!)

 

[alex robinson]

Every cheap set of compressor accessories comes with what is described as a paraffin spray gun. I think that meets the intent of what you describe in terms of jet.

It would appear to work on the principle you say you do not want (air entering and pressurising the vessel displaces the liquid) and would be made of unsuitable material but might give you some ideas.

Another place to look is Gloria sprayers - normally they are the pump up plant sprayer idea, but I think they offer a model that can be pressurised by an external supply (and has a built-in properly tested pressure relief valve so you do not accidently make a bomb. They offer a wide variety of nozzles as well as a wide range of non-metallic materials. They would probably make a custom nozzle for you if you could describe flow rate and pattern to them.

It did come with a paraffin gun and that is an option. Certainly didn't dribble! So it doesn't have one of the problems of the DIY option, but it would mean having to carry the water with the gun. Maybe it is just the budget set, but the paraffin gun seemed really unwieldy.

I will have a look at the Gloria sprayers. I am sure there is another group of people with weird requirements about materials for sprayers!

 

[alex robinson]

Have a word with your health and safety officer or HR
If the problem is explained see what they can do
Sorry to say this but my CYA (cover your backside) has just kicked in and I can see you personally being held responsible for bad practice / contaminated tests
And all the above as well as your work mate not being able to claim off the firm because you implemented a non approved method
If I am way out of line then
My most humble apploigies.

Not out of line at all. I appreciate the sentiment. H&S agree (unsurprisingly) that the old method isn't any good. Working out the new approach is a bit specialised for them however. We will need to run new calibrations and blanks, but we have reasonable freedom to develop new protocols so long as they get the job done. (I will post some pictures of a very fun new technique involving a digger we developed recently once everything is set up)

 

[alex robinson]

Could you assess what pressure and flow rate the standard squeezy bottle delivers?

It strikes me that a KISS system, of a gravity-fed spray head with a simple on-off valve could deliver similar performance. It all depends on if the available height will give enough pressure head. Put the tank on the roof and relocate the lab into the basement.

That is tempting, just to see the look on the facilities guys faces if we suggested that! The volume required isn't huge, but I think it would have to be a 2 story set up to get the pressure needed and realistically that is unlikely.

 

[XTiffy]

What might be possible is some sort of foot control, which would remove the hand RSI element. Even to the point of the "spray nozzle" being on a support arm.

 

[pe2dave]

Interesting question. Having suffered trying to get container 'clean' (your definition) and failing for days,
I can see the sprayer, tubing, compressor having to be investigated / assessed.
You might look to the medical field (or military) for appropriate filters on the output.

 

[ChaiLatte]

As the standard squirt bottle is around 500ml capacity, maybe something like a hospital IV drip bag atop an adjustable pole could suit. Put it between two spring or weight assisted boards or something like a weighted log tongs (https://www.amazon.co.uk/VEVOR-Skidding-Tongs-inch-Claw/dp/B0CDW62Y5X)* so the mechanical squeeze compensates for lack of elevation and still produces the pressure required.

If you produce the pressure by a different means to compressed air, that eliminates all the air filtration requirements. The other option is to have the water in a bladder that is pressurised by the air. Then the air could be as dirty as you like since it never contacts the liquid.

* or mount the drip bag whoopie cushion-style on the chair. Bonus is that you can work when sitting down.

 

[alex robinson]

Interesting question. Having suffered trying to get container 'clean' (your definition) and failing for days,
I can see the sprayer, tubing, compressor having to be investigated / assessed.
You might look to the medical field (or military) for appropriate filters on the output.

"Clean" is one of those things that entirely depends on what you are concerned about! I am not a plastics person, normally working on pesticides or metals. Both of those are easy - acid washing for metals and organics such as acetone for the pesticides. Even microbial cleanliness for molecular biology isn't really hard.

Plastics work is difficult as 1) It is everywhere, especially in the form of microplastics. One of the projects is measuring the levels in drinking water, so any kind of washing has to be done with liquids that have been multiple filtered. 2) The majority of the items one might want to use to make equipment with are made of plastic. Tubing valves etc all therefore have to be made either of non plastic materials like metal or glass, or out of an obscure and expensive polymer that can be ignored in the subsequent analysis.

 

[alex robinson]

As the standard squirt bottle is around 500ml capacity, maybe something like a hospital IV drip bag atop an adjustable pole could suit. Put it between two spring or weight assisted boards or something like a weighted log tongs (https://www.amazon.co.uk/VEVOR-Skidding-Tongs-inch-Claw/dp/B0CDW62Y5X)* so the mechanical squeeze compensates for lack of elevation and still produces the pressure required.

If you produce the pressure by a different means to compressed air, that eliminates all the air filtration requirements. The other option is to have the water in a bladder that is pressurised by the air. Then the air could be as dirty as you like since it never contacts the liquid.

* or mount the drip bag whoopie cushion-style on the chair. Bonus is that you can work when sitting down.

Unfortunately that involves a lot of plastics!

The PTFE squirt bottles were an acceptable compromise (apart from the causing injuries aspect!) They prevented PTFE from being included in the analysis, but were at least available off the shelf.

Another option we have considered has been big glass syringes using a motorised syringe pump. The flow rates from syringe pumps are normally measured in ml / hr though so it would need a custom device, perhaps involving a drill driving a section of threaded rod.

 

[alex robinson]

What might be possible is some sort of foot control, which would remove the hand RSI element. Even to the point of the "spray nozzle" being on a support arm.

That would be ideal. If it could be electronic rather than having to have bottles or tubes on the floor (decontamination nightmare when refilling) that would be even better.

 

[BillK]

Would the squeezing action of a gun trigger not make the RSI worse? When I had severe hand problems I first noticed it using sprayguns. The weight of a loaded gun and the air hose also need considering I should think.
If you remove the air cap from a gun it'll squirt a jet but quite a fine one. Also you'd be refilling the cup often. Although a suction type gun like underseal or grit blaster guns could draw from a container via a tube. Takes quite a bit of compressor power to drive a grit gun though.

Better quality air filters should state their filtering, mine is 5 micron I think. Filters/traps are often combined with a pressure regulator.
Helps to run the filter and gun (or tool) further away from the comp, so moisture from the warmer damp compressed air has more chance to condense out. I had copper lines with a ~5 foot vertical drop leg, ball valve at the bottom. Hardly any moisture hit the reg/trap, it all condensed out before it got there. Gives the trap less work to do.

There are foot operated pressure valves, maybe a system could be built around one.
There's 'pressure pot' spray guns where instead of an on-gun cup it draws from a pressurised container. Maybe something similar could be adapted with a foot valve and a fixed gun or jet/outlet, no hand triggering then.

 

[Fitzroy]

I think any sort of paint sprayer etc will supply too large a volume. Those lab squirty bottles will be doing a few ml at a time, paint sprayers are more like a litre/min. Perhaps an air brush is more the sort of equivalent flow rate and would give a buyable solution.

As you say putting air pressure onto the squirty bottle will give a long lag and an annoying dribble afterwards. A fish-tank air pump with a remote (foot) switch and a filtered supply onto the PTFE squirt bottle was on my mind, but it would be very heath robinson and suffer this issue.

I think a gravity fed system with 1/4" PTFE tubing and a 12V DC solenoid valve (something like this) operated from a foot switch could be fairly easily constructed, and would give good controllability.

 

[alex robinson]

Would the squeezing action of a gun trigger not make the RSI worse? When I had severe hand problems I first noticed it using sprayguns. The weight of a loaded gun and the air hose also need considering I should think.
If you remove the air cap from a gun it'll squirt a jet but quite a fine one. Also you'd be refilling the cup often. Although a suction type gun like underseal or grit blaster guns could draw from a container via a tube. Takes quite a bit of compressor power to drive a grit gun though.

Better quality air filters should state their filtering, mine is 5 micron I think. Filters/traps are often combined with a pressure regulator.
Helps to run the filter and gun (or tool) further away from the comp, so moisture from the warmer damp compressed air has more chance to condense out. I had copper lines with a ~5 foot vertical drop leg, ball valve at the bottom. Hardly any moisture hit the reg/trap, it all condensed out before it got there. Gives the trap less work to do.

There are foot operated pressure valves, maybe a system could be built around one.
There's 'pressure pot' spray guns where instead of an on-gun cup it draws from a pressurised container. Maybe something similar could be adapted with a foot valve and a fixed gun or jet/outlet, no hand triggering then.

That is excellent to hear about the filters. Thank you. I could look up and see that such things existed but had no feel for how practical or specialised an item they were.

The hope regarding the RSI is that we could find one with a gentle trigger spring and so instead of multiple squeezings of the bottle (needs to be surprisingly forceful to get a decent jet), there would be 1 soft pressure on the trigger.

I liked the option of the gravity fed type gun as all of the pressurised bits (post air filter) could be metal. Apparently the nozzle has to be moveable - a fixed outlet isn't practical

 

[alex robinson]

I think any sort of paint sprayer etc will supply too large a volume. Those lab squirty bottles will be doing a few ml at a time, paint sprayers are more like a litre/min. Perhaps an air brush is more the sort of equivalent flow rate and would give a buyable solution.

As you say putting air pressure onto the squirty bottle will give a long lag and an annoying dribble afterwards. A fish-tank air pump with a remote (foot) switch and a filtered supply onto the PTFE squirt bottle was on my mind, but it would be very heath robinson and suffer this issue.

I think a gravity fed system with 1/4" PTFE tubing and a 12V DC solenoid valve (something like this) operated from a foot switch could be fairly easily constructed, and would give good controllability.

I am perhaps being sloppy with language. I am meaning some sort of gravity fed device that is linked to a compressor. I have used an airless sprayer plenty in the past, but never tried any of the compressor type options - hence the plea for advice!

The "drill a hole in the ceiling" option is still tempting, but will unfortunately be a no go, and any smaller header height will be too feeble.

 

[Ollie78]

I am thinking you could contact someone like Sames Kremlin, they make air assisted airless sprayers but will also outfit full on robot controlled production lines with spray equipment and dosing certain amounts etc.
I suggest they, or a similar company will be able to supply a products which would do exactly what you need and also be certified for lab use with the filtration etc.