Pin Valve maintenance: How it works, how to fix it if it doesn't.

Some background:
The standard pin-valve as we know it, for the average paintball marker, serves as both a way to attach the tank to the ‘Gun, and as a sort of automatic on-off valve. Besides that, it must safely contain pressures up to 1800 psi, in the case of standard Co2 tanks, or 3000 psi in the case of removable High Pressure Air system tanks. The pin valve also provides a place to mount what’s known as a “burst disc” safety device. All this, and put up with the normal bumps, bangs and abuse the average paintball player dishes out. To keep the tank and valve in top working order, and to safely repair malfunctioning valves, all it takes is a bit of know-how, and some common sense.

The Burst-Disc:
The burst disc is a small, copper disc of a specific, known hardness and strength. It is held in a specially-designed port on the side of the pin or on-off valve, by a short threaded plug or “bolt” that is drilled with several passages. The disc is sealed to the port by a small thin Teflon washer. The “bolt” is drilled, so that in the possibility of the burst-disc rupturing, the escaping gas is equally vented in at least two opposing directions, so that it doesn’t become a “rocket” and fly across the field and injure someone.

The disc itself is designed to hold the normal working pressure of the tank, but is thin enough that in the case of an over pressure situation, the disc will rupture long before the tank or valve is damaged. For example, most Co2 tanks have a disc rated to burst at around 2200 to 2500 psi, the specific rating is usually stamped directly on the copper disc itself. A 3000 psi “nitrogen” tank usually has a disc rated to 5000 psi. Now, the copper is a metal, and like all metals, is subject to fatigue form the pressure/depressure cycle. So an old valve with a lot of hard use could possibly burst when no gross overpressure situation is present; the metal of the burst disc merely weakened from use. When the tank is ‘hydrotested’, the service technician will usually also replace the disc as a precaution.

If your disc blows, replacements are easy to install, but care must be used to ensure they are in properly. Remove the “bolt” or plug, and you’ll see the ring remnant of the blown disc. Use a toothpick or similar tool to remove the copper ring. Under that, there should be a thin Teflon washer, leave it in place. If the washer is missing, check to see if it came out with the copper. Make sure the washer is in place! New discs are available from most manufacturers, and any decent Paintball shop should have them in stock. Make sure the disc has something printed on it, such as “2200” or “2500”, this is the burst rating in PSI. If the disc is blank or says anything lower than ‘1800’ or higher than ‘2500’, do NOT use it! Simply slip the new disc, printing out, into the place of the old one, and reinstall the ‘bolt’. Tighten it carefully, but be sure not to overtighten or strip it. Two fingers on the wrench is about right.

Inside the Valve:
A “true” pin-valve has a solid brass central core with a thick, high-durometer urethane sealing element. The pin is preloaded against the seat by a short, stiff spring, held in from the inside by a threaded plug. Once the tank is filled, the internal pressure also holds the pin in place, increasing the sealing force. The most common causes of leaks in a ‘true’ pin valve, are a bit of grit or dirt getting trapped between the valve seat and the sealing element, or “ring”, and the ring itself cracking from the intense cold of the liquid Co2. In the case of the dirt or grit, often the leak can be solved by “burping’ the pin-valve by forcing it open briefly with a non-marring tool, such as the handle of a plastic toothbrush or a short dowel. The released gas may dislodge the grit, allowing the element to seal again. Unfortunately, occasionally the grit will actually embed itself into the sealing element, or worse yet, dent the valve seat inside the pin-valve itself. In these cases, and if the element itself is damaged or cracked, the valve will have to be removed from the tank for repairs.

“Schrader”-style pin valves use a similar valve body and burst disc as the “true” pins, but the sealing element is, basically, a tire valve. These are not as reliable or durable as a ‘true’ pin, and are accepted as frequent leakers. However, they do have two benefits over the solid-core pin; they can be repaired without removing the valve from the tank, and they are usually somewhat less expensive. However, personally, I don’t like the idea of 800 to1200 psi being held in by that tiny valve and thin, shallow threads. If you have a choice, opt for the “true” or solid-core pin valves.

The third, though less-frequently seen, valve is the “Super Flow” valve, originally marketed by Smart Parts, now sold by the manufacturer, Pneu Ventures. These use a large-diameter central “pin” which is actually shaped like a top-hat, and seals against a Teflon ring around the rim. This design increases the airflow rate though the valve, and is rebuildable from the outside; it doesn’t require removal from the tank. (Of course, the tank MUST be completely depressurized before disassembling the valve.)

Removing a Valve:
Update, Fall 2007:

Unfortunately there have been some accidents involving incorrectly or improperly repaired
tank valves in the ten years since this article was originally written. Newer valves have
been redesigned for improved safety and easier repair, but now should only be serviced by
a trained and authorized technician. If you have a leaky CO2 pinvalve or malfunctioning
HPA regulator, a blown or missing burst disc, or any other issue with your air tanks,
please take them to an authorized service center for removal, repair or replacement.

All contents Copyright 1998, Airsmith Services. All rights reserved.
User assumes all risk pertaining to the use or implementation of the information contained herein.
Updated October 2007.