No, it would be practically impossible to damage LEGO pneumatic elements by overpressurizing them.
It turns out that LEGO pneumatic pumps actually have a very simple "slip" mechanism that prevents overpressurization. Once the pressure reaches about 35-40psi (the exact threshold varies slightly pump by pump) the rubber plunger disk will give way and bend ...
Key components would be Technic, Gear Rack 1 x 4 and Technic, Gear Worm Screw
Application of said parts are left as an exercise for the reader, though since OP says they're not using Technic, this might be a moot answer.
In this discussion at LUGNET the conclusion seems to be that you could use dry graphite if you are comfortable with graphite powder everywhere. Else you should try lithium grease or canola oil.
There is also a serious warning about using hydrocarbon oils that could damage the rubber seals inside pistons and the rubber air tubes.
One poster also noted that ...
According to various sources, LEGO pneumatics is not designed to work above 3 (or maybe 4) bars of pressure, so your setup might have been damaged by the overpressure.
If you can "press on the the pumps in certain ways" then I would recommend starting your investigation there. As to actually locating the cause of the leakage, I have five main methods in ...
I tried many designs I found
A quick Google search resulted in the following designs. Have you tried them all?
Philo's pneumatic valve:
Sariel's Servo Valve:
Tamas Juhasz's small autovalve with compressor:
Technic-Dragon's Compact Pneumatic Autovalve:
Bonus entries, not using exclusively PF motors, but could be adapted to:
You wrote you would like to hear an answer that is more definitive as a guess. I guess then we can accept Sariel as a definitive source, and he writes here:
There is no risk of anything blowing up. If you’re using Lego pumps, they will simply lack the power to keep pumping once a critical air pressure is reached. There is a risk, however, that your Lego ...
I see two main problems that need to be adressed here.
Intrusion of liquids into the pneumatic system
Intrusion of solid particles into the pneumatic system
To filter out solid particles, namely baking soda, a fine mesh could be used, either alone or in multiple layers.
To get rid of droplets, some absorbing material such as cotton could be inserted ...
LEGO Pneumatic system could consist of different elements like hoses, switches, pumps, cylinders and T-junctions. Each one may need different approach.
I could think of several ways of testing these issues.
First one might be a little hard, but depending on the issue could be a quick solution. This would works for any pneumatic element. You need to get ...
You will not destroy the air tank using standard LEGO components. I don't know what it's structural limits are, but I can tell you that the weakest link in the pneumatic system in my experience is the connection between the rubber pneumatic tubes and plastic inlets. Under high pressure, the tubes will simply pop off before any of the components will actually ...
Since the compressor produces compressed air, it would certainly work, given you build adequate fittings and take precautions against overpressurization.
LEGO pneumatics have been tested to withstand as much as 8 bars or 120 psi, but you definitely should plan with safety margins. If your compressor can produce higher pressures, I'd suggest building in some ...
You shouldn't use a CO2 tank with the pneumatic cylinders because it could pop the pistons out of their casings. I would take some pop bottles (2 liters), glue some T-shaped connectors in the lid and fill it with air using bike pump.
Warning. Do Not Go over 100psi with these pop bottles or they will explode. So wear saftey glasses when filling them.
I was going to recommend lubricating the pistons, but seeing you already did exactly that, I can only say you should try to isolate the source(s) of the problem.
Since you have at least one working cylinder, the compressor and the feed tubes should be all right. This leaves the following possible points of failure: switches, subsystem hoses, working ...
I do not own such piece, so cannot tell if they all are broken by this time. However I have a suggestion regarding acquiring a replacement.
Bricklink is a dedicated to trading just LEGO items, so I can recommend to look here for replacement. While some of the sellers do not check functionality of all the items they sell it is considered items should be in a ...
The pneumatic system's limit is three bar (40psi). After that point, the hoses will pop off the ports. I don't think you could explode the airtank very easily with a real compressor. My guess is that it would start deforming around the 5-10 bar range, and only explode once it was bordering on spherical :P.
Your question is general, so I'll try to answer generally, but I'll use the pneumatic cylinder as an example since you mentioned it.
If applicable, the first thing you'll want to do is break down the part(s) as much as possible. Open up the pneumatic cylinder and separate out the parts:
I'd recommend cleaning everything separately, lubricating the ...