"What parts do I need?"
"Can I fire three guns from one valve?"
"What’s difference between an MAV-2 and an MAV-3?"

This article aims to address many of the cannon set up issues confronting the first time builder and battler and to be a resource that can benefit everyone in the hobby - Big Gun, Small gun, and those in other scales. All these Captains use Clippard parts. The best piece of advice anyone can give is this.

"If no body does it the way you're going to try first - there's a reason for it,
so do it like everyone else".

If you think you have some new fang-dangled way of doing something that is cheaper and/or easier with less parts than what people have come up with to date – try it on your second ship. By the time you’ve finished your first ship, you’ll know why it’s done a certain way. By all means experiment and design new and different things. Creativity and ingenuity is what made this hobby possible in the first place. That and the use of Clippard parts.

2.0 Operation of Guns.
While out of the scope of this article, it is beneficial to have some knowledge of how the hobby’s various gun designs work. There is a lot of good information on websites and therefore no point in reproducing what is already available.

The same firing set up is required for these two Big Gun cannon systems as for the multiple gun system for piston selector guns.

3.0 Valves.
All the Clippard valves used in the hobby essentially function in the same manner. One of the ports (a tapped hole which requires a fitting) is an inlet port. When the system is "live" this side of the valve is kept at high pressure (120 – 150 psi depending on club rules). The other exit port(s) is(are) a tapped hole(s) in the side of the valve. When the servo arm or custom made cam pushes the stem of the valve it opens allowing the gas to flow through until the servo retracts and the internal spring in the valve closes it, thus stopping the flow of gas.

Note: If you compare the two illustrations of the different valves you can see the exhaust holes in the stem of the MAV-3. They are consequently not in the MAV-2 valve.

An example of the difference is to consider two different scenarios. Firstly an MAV-2 with a 140psi (say) supply at the inlet port and a small length of hose with a capped end on the exit port. (This is effectively an accumulator tank, refer section 8.0). If the valve stem is pressed (opened) the pressure in the capped tube will rise to 140psi. The valve is then closed and the pressure in the exit line will remain at 140psi until the end cap is removed. Then consider the same set up but using an MAV-3 valve in place of an MAV-2. The pressure of the exit line will still rise to 140psi, but when the valve is closed, the gas in the exit line will exhaust to the atmosphere through the stem of the valve thus giving no pressure (atmospheric) in the exit line.

Another way of looking at it is that you can blow gas into the exit port of a closed MAV-3 and it will exhaust out the stem hole. You cannot blow gas into the exit port of an MAV-2.

Harder firing cannon can be accomplished by five methods. "Tweaking" the gun, using a more efficient design of cannon, or installing longer barrels - all of which are outside the scope of this article. Alternatively by supplying more gas pressure (greater than 150 PSI) which is illegal under all model warship combat club rules, or by supplying more gas flow at a legal pressure. The best methods of the latter are; increasing the Internal Diameter (ID) of the gas supply line, shortening the length of the gas supplying line between the valve and the cannon, and installing an accumulator (refer section 8.0) as close as possible to the constant high pressure side of the firing valve.

You can do a simple experiment for yourself. Take the longest length of 1/16" ID tube you have and try sucking or blowing through it. Then take a short length of the same diameter tube, say 2" long and try the same with that. You will find that it’s much easier to breathe through the shorter piece of tube. In other words, the longer it is the harder it is to get any gas. This is an example of viscous friction.

Note: You cannot use this method for firing a single Big Gun "Indiana Cannon" or "Arizona gun". See section 6.0.

Figure 5. The simplest gun set up. A CO2 supply (12g CO2 canister and normal regulator in this case) an MAV-2 valve and a piston selector cannon. Note the use of 1/8" hose instead of 1/16" hose. BB holes through a piece of 3/8" balsa.

5.1 Firing Multiple Piston Selector Guns.
If you want two or more piston selector guns to fire simultaneously you have to use a different set up for a number of reasons. Firstly you won’t get sufficient gas flow for two guns using one MAV-2 valve, even if you use 1/8" hose and barbs for all your plumbing. See fig 6. Secondly you will get uneven gas flow to each gun depending on which gun is "tweaked" to fire harder (one of the guns will also fire first). Thirdly this makes it very difficult, if not impossible, to tweak the guns. You certainly can’t do it individually unless you mess around with the plumbing. It is also not advisable to try operating two valves with one servo as this gives less than perfect results as most servos just aren’t strong enough to push two valves. Yes you could have a servo splitter using two servos to operate two guns, but it will be cheaper to buy the proper Clippard parts and another servo is just another electrical thing to go wrong when Clippard parts are so reliable.

Figure 6. Two Piston Selector guns fired from one valve. Not recommended, but possible. See Section 7.0.

The best, most reliable method of firing two or more piston selector guns simultaneously is to have one servo depressing one valve which in turn fires multiple guns. Mount the firing servo and an MAV-3 in a custom made bracket so that the servo can actuate the MAV-3 to fire the guns. The exit line from the MAV-3 will then go to a "T" (three barbs) or "X" (four barbs) Clippard fitting for a two or three gun system respectively. If more than three guns are required e.g. King George V class ship or KGV as they are known (which has the potential to be armed with four guns in its aft turret) a Clippard manifold may be required to get even pressure in all gas lines to the guns. Remember also that the shortest possible gas lines should be used for the most rapid firing.

Each gun then requires another MAV-2 to feed the gas to the gun (as described in firing a single gun) which is actuated by a pilot actuator. The most commonly used actuator for an MAV-2 is the MPA-3. The stem and threaded body of the MPA-2 is screwed into the large threaded hole in the MPA-3. When the MPA-3 gets a burst of gas from the servo operated MAV-3 the internal piston pushes the stem of the MAV-2 that it is screwed in to. This in turn fires each gun. With this set up multiple guns can be reliably fired from one servo.

If an MAV-2 were used in place of the MAV-3 in this case, the pilot actuator would be permanently depressed as the gas cannot bleed from the exit line of an MAV-2, thus holding the gun valve (MAV-2) open letting 140 psi CO2 escape through the gun.

6.0 Firing Valves for Big Gun Cannon.
Traditionally all Big Gun cannon are fired with a pilot actuator. An MPA-3 for Arizona guns and MPA-7 for Indiana cannon. For the reasons outlined in sections 3.2 and 5.1, three way valves must be used to trigger these to actuate. If a two way valve is used, the MJV-2 (Arizona) or MPA-7 operated ball valve (Indiana) will remain open and bleed all the CO2 from the bottle.

Only one MAV-3 is required to fire multiple Indiana cannon (e.g. three forward turrets on an HMS Nelson class battleship and many Japanese cruisers) or Arizona guns.

There is a very good article on the North Texas Battle Group website on Safe, Effective CO2 Delivery

7.0 Alternatives.
A Hybrid of the system (used successfully in a 1/96 "Big Gun" destroyer) is illustrated below. This is an example firing two piston selector guns with one valve. In this case the gun firing valve is an MLV-2 as it has approximately 3.5 times the flow rate of an MAV-2. 35 scfm (standard cubic feet per minute at 100 psi) as opposed to 6.8 scfm of an MAV-2. As stated previously this is a little undesirable as tweaking the guns is difficult due to both firing simultaneously and slightly different gas flow to each gun. This is overcome to a great extent by the increased gas flow of the MJV-2 and was necessary due to space and weight constraints in these small ships.

Figure 7. Two unmodified piston selector guns fired from one MJV-2 valve with accumulator tank, actuated by an MPA-7. An MPA-3 may be used in its place.

8.0 Accumulator Tanks.
Clippard also offer a range of different size accumulator tanks, or Air Volume Tanks (AVTs). The advantage of these tanks is to have a secondary source of compressed CO2 close to the guns to facilitate hard rapid firing. In most cases long tubes from the bottle do not supply sufficient gas to sustain hard, rapid firing of piston selector guns. It is also good practice to install a one way valve or Miniature Check Valve (MCV) on the input port of the accumulator tank. This ensures that the high pressure gas cannot bleed from the accumulator tank to other parts of the system (specifically other guns when they fire and thus reduce the pressure in that gun’s accumulator tank).

Figure 8. An Air Volume Tank (AVT).

8.1 Regulators.
Fine tuning of a ship’s firing mechanism may require varying the pressure slightly of one or more parts of the system. A Clippard Miniature Adjustable Regulator (MAR) may be used. Essentially the input line is at the end of the cylinder and the exit port is in the side. The output pressure is adjusted by turning the knob on the end. This moves an adjustment mechanism inside the regulator, which adjusts the force of the spring thus regulating the pressure.

Figure 9. Miniature Adjustable Regulator. MAR-1.

Clippard manufacture Miniature Toggle Valves (MTVs) that can be used for this. Only one is required per ship. The single outlet line from the tank regulator is plumbed into the inlet port (end of the cylinder) of the MTV-3. Only the bottom (closest to the inlet port) of the two exit ports is plumbed. This supplies gas to the rest of your system. When the ship is armed the gas flows in the inlet port and directly to the rest of the system. To disarm the ship’s guns, flick the toggle to the opposite side. This closes the inlet port so no gas can flow through the valve and at the same time, vents the exit port of the valve through the top port to depressurise the system.

Figure 12. A Miniature Toggle Valve. MTV-3.

9.0 Conclusion.
Clippard parts have been used in R/C model warships, literally, for decades. They have stood the test of time – that’s why they are still used almost exclusively in all formats and scales. Big Gun, Small Gun, 1/144, 1/96, and 1/72.