Safe, Effective CO2 Delivery

Special contribution from Phil Sensibaugh, of the Midwest Battle Group

Obviously, the whole point of warship combat is to be able to sink your opponents by firing ball bearings at their ships.  Hulls are designed specifically to allow penetration, and damage control countermeasures are restricted so as to make the threat of sinking a very real possibility for any combat ship.  Even so, a weapon system that is capable of punching a hole through thin balsa sheet is going to also have the potential to inflict harm on people or animals, or damage property if certain safeguards are not built in, and safe practices followed.  While part of the fun of building models – combat or not – is in the “tweaking”, experimenting, and learning while you try to make something work, there are some aspects of warship design where it’s best to go with a proven solution.  In particular, those areas of warship construction that involve safety – the prevention of injury or property damage – should not be built by “trial and error” methods.  It’s one thing to waste a bunch of your time, trying a new and clever method of building a hull, controlling motors, rotating guns, etc.  It’s quite another when the potential consequences of error can involve serious injury.  Working with gasses under pressure certainly has the potential for causing injury and/or damage if proper care is not taken in the design, construction, and operation of these systems.

There is no substitute for proper handling practices.  This includes the wearing of eye protection by all persons – spectators and participants alike – that are in the area where combat warships are being operated or worked on.  Armed combat warships should be handled just like firearms – with respect!  In addition to requiring eye protection, the captain of a combat warship must always be aware of where his barrels are pointing, as well as who or what might be in an area where they might be hit by a stray shot.  Even when you’re sure your magazine is empty, there still might be one more ball rolling around, that hasn’t been fired yet.  Splinters, dirt, or other foreign objects can find their way into a cannon, where they could be unintentionally propelled by a gas release through the barrels.  Everybody has heard horror stories about huge negligence lawsuit awards – and any kind of model warship combat practiced without appropriate safety considerations is just a lawsuit waiting for a plaintiff!

It is the responsibility of of every warship captain to make sure that his ships’ systems are built in such a way that the systems themselves are as inherently safe as is reasonably possible.  Special thanks to Phil Sensibaugh of the Midwest Battle Group for providing the information that went into this article.  Phil’s design is the result of sound engineering practices and extensive warship building and combat experience.  This system represents the state of the art in combat warship CO2 delivery systems.  Figure 1 illustrates the basic system, in the “armed” state, for a typical 3-cannon system.  In this system, the cannons labeled “A” & “B” are fired together, while cannon “C” is fired by itself.  4-cannon systems (i.e. 2 forward, 2 aft) can be built by extending this design, adding additional components in parallel with “C”, just as “B” is in parallel with “A”.  Likewise, a 2-cannon system (1 forward, 1 aft) can be built by removing “B” and its associated components, so that “A” and “C” each fire singly.

WARNING:  Always wear eye protection when working with charged CO2 systems.

Figure 1.
Basic CO2 Delivery System Schematic (Ready To Fire).


Parts List

The following table lists individual parts and quantities required for a typical systems of 2, 3, or 4 cannons.  Prices are list prices as of January, 1999, in Dallas, Texas.  Prices may vary by location, and may be subject to change.  Quantities depend on individual ships’ system requirements, however this should give you a “ballpark” idea of the costs and items involved in outfitting a ship for combat.

Item  Number

Quantity 2-Cannon

Quantity 3-Cannon

Quantity 4-Cannon

Part Number



1111(various)$35.00 – $70.00, depending on sizeCO2 bottle, anti-siphon, on/off valve
2111(various)$16.00 – $40.00, depending on weightRegulator, tank
3111SMTV-3 (Clippard)$8.45Safety valve
4234MAR-1 (Clippard)$9.90Adjustable regulator
5222SMAV-3 (Clippard)$9.15Firing valve – 1 per cannon
(or cannons fired together)
6234MCV-1 (Clippard)$3.65Check valve ( 1 per cannon)
7715002-2 (Clippard)$5.75“L” fitting (package of 10)
8515002-3 (Clippard)$5.75“T” fitting (package of 10)
9515002-4 (Clippard)$5.75“X” fitting (package of 10)
10234MPA-7 (Clippard)$6.45Actuator (normally supplied with cannon)
11234n/an/aAccumulator (part of cannon)
12111n/an/aServo wheel, modified to operate SMAV-3 firing valves
131113814-7 (Clippard)$8.65Urethane tubing (50 feet/roll)
14 (not shown)515000-4 (Clippard)$0.42Hose clamps (package of 10)
15 (not shown)715004 (Clippard)$2.35Female/female hex connectors (package of 10)
16 (not shown)4211752-2 (Clippard)$3.2510-32 X 1/16″ hose fittings (package of 10)
17 (not shown)(optional)(optional)(optional)11999 (Clippard)Short coupler, 10-32 male/male (package of 10)
18 (not shown)23415006-1 (Clippard)$3.401/8″ – 27 NPT to 10-32 adapter (typically supplied with cannon)
19 (not shown) (optional)(optional)(optional)15040 (Clippard)$4.2010-32 swivel fitting (package of 10)
20 (not shown)4 (optional)6 (optional)8 (optional)MQC-V3 (Clippard)$1.50Quick disconnect (male side)
21 (not shown)4 (optional)6 (optional)8 (optional)MQC-F2 (Clippard)$1.55Quick disconnect (female side)
22 (not shown)(optional)(optional)(optional)11761-2 (Clippard)$0.50Buna-N gaskets (pack of 50) – all fittings come with 1 gasket per male connection.
23 (not shown)(optional)(optional)(optional)11761-1 (Clippard)Lead gaskets (pack of 10)
24 (not shown)(optional)(optional)(optional)11755 (Clippard)$1.4510-32 plug fitting (package of 10)
26 (not shown111n/an/aLoctite thread sealer (bottle)

Technical Notes, By Item Number:

1.  CO2 bottle (tank), with shut-off valve, 1 per system, size depends on space constraints of the hull.  The tank provides the source of compressed CO2 for the entire system.  Note that the bottle needs to have a ball or needle valve, that has a knob or handle so that you can open or close it.  It is important to get a tank with an on-off knob, and an anti-siphon tube to draw gas from the top of the tank, near the shutoff valve.  The anti-siphon valve helps to make sure that only gaseous CO2, not liquid, is discharged into the delivery system.  Liquid CO2 can damage the system.  Tanks with the pin valve (shrader valve like in a car tire) commonly used in paint ball games do not work well in this hobby.

CAUTION:  Pressure in the tank may prevent the tank from unscrewing from the regulator by hand.  If a wrench is used, the O-ring on the regulator will be damaged nearly every time the tank is removed, and the tank will leak the next time it is installed.  To prevent O-ring damage, flip the SMTV-3 safety valve OFF, then turn the knob on the tank off, then cycle the SMTV-3 safety valve ON and OFF several times to vent all pressure from the lines before attempting to remove the tank from the regulator.  This will eliminate damage to the O-ring in the regulator, and the tank will unscrew easily by hand.

2.  High pressure regulator, 1 per system.  This regulator keeps the CO2 at a constant maximum pressure (140 psig, typically) throughout the system.

3.  SMTV-3 (Clippard) valve, 1 per system.  This is the main safety shut-off valve for the entire system.  Ports on the valve are marked “IN” – which connects to the tank via the high pressure regulator, “OUT” – which connects to the rest of the delivery system, and “EXH” – which is an exhaust port.  In the “ON” or “ARMED” position (unmarked), the valve provides a path for gas to flow between the “IN” and “OUT” ports.  In the “OFF” or “SAFE” position, the valve closes the “IN” port, and vents the “OUT” port to the “EXH” port.  This venting is critical to safety in the Big Gun warship cannon CO2 delivery system application – this allows us to vent off pressurized CO2 when the system is disarmed, making it impossible for the guns to fire.  This switch is configured to be panel mounted – it is essential that it be mounted on the ship in a position where it can be reached easily, with the ship buttoned up.  Also, it’s a good idea to put a dab of bright red paint on the panel next to the switch, as an obvious indicator of which position is “hot”.

4.  MAR-1 (Clippard) adjustable regulator, 1 per cannon.  This regulator “steps down” the high pressure output of the “main” regulator (item #2), to a lower pressure that is delivered to the cannon accumulators.  The use of a low pressure side to this system is an essential safety element of the system and should not be omitted.  While a single MAR-1 regulator may suffice for an entire system, inconsistent pressures between the cannons may result.  Using one MAR-1 per cannon allows flexibility to control the pressure that is actually delivered to each cannon, and allows you to “tweak” them individually for optimum overall performance.  Regulator “A” serves cannon “A”, etc.

5.  SMAV-3 (Clippard) valve, 1 per gun (or guns that are to be fired simultaneously).  This valve has 3 ports, marked “NC” (Normally Closed), “OUT”, and “NO” (Normally Open).  Connect the “NC” port to the high pressure side of the system, so that the SMTV-3 safety switch (item #3) is between this junction and the tank/regulator (items #1 & #2).  Connect the “OUT” port to the input of one or more cannon’s MPA-7 actuator (item #10) – connect multiple cannons to a single SMAV-3, where you want to fire them simultaneously.  In the “unpushed”, or “normal” position, ports “NO” and “OUT” are connected, allowing the MPA-7 to vent through this path, while “NC” to “OUT” is closed.

CAUTION:  Connecting anything to the “NO” port of the SMAV-3 can cause the MPA-7 to not vent when firing pressure is release, and hold the connected cannons’ ball valves open.

When the switch is pressed, the configuration reverses and gas is allowed to flow between “NC” and “OUT” – gas flow through this path activates the connected cannons’ MPA-7 to operate, firing the cannon(s).  When the firing valve is released, the MPA-7 actuator vents through the SMAV-3 valve, closing the cannons’ accumulator ball valves.

6.  MCV-1 (Clippard) check valve, 1 per cannon are required.   Check valves allow gas to flow only in one direction, as indicated by an arrow marked on the side of the valve.

The check valves provide two functions.  First, they isolate each cannon so that if only one cannon is fired the pressure in the other cannons will be maintained, allowing them to fire with full force.  Without the check valves, when one cannon is fired and a second cannon is fired immediately thereafter, the second cannon will fire with very little force, since the pressure in the lines drops as the first cannon’s accumulator is recharging.  Also, the accumulator of any un-fired cannons will try to refill the just-fired cannons’ accumulator(s), reducing the pressure available for another shot until all cannons’ accumulators have equalized their pressure.

WARNING:   These valves are an essential part of the system’s safety engineering and should not be omitted.  Likewise, this diagram should not be modified in any manner except for the addition of more identical components to support more cannons (or the removal of excess components to support fewer cannons) since the diagram depicts a 3 cannon system.

The second function of the check valves is safety, allowing the accumulators of each cannon to discharge when the safety valve (SMTV-3) is in the SAFE position.  The safety system works in the following manner:  The check valve connects to the high pressure line from the main regulator to the individual cannon.  With the SMTV-3 safety valve in the ARMED position, high pressure gas shuts off (reverse biases) the high pressure check valve.  Lower pressure gas from the MAR-1 flows through the low-pressure check valve and fills the cannon accumulator, but can not get through the reverse-biased high pressure check valve.  If any cannon in the system is fired, causing line pressure to drop, the MAR-1 functions as a “low-pressure check valve” and holds the pressure in the accumulators of the un-fired cannons.

When the safety switch is set to the SAFE position,  the supply of CO2 is removed from the system and the high pressure exhausts through the SMTV-3 safety valve’s EXH port.  Once the high pressure CO2 is exhausted, the check valve opens (forward-biased) and the low pressure CO2 (which is now at a higher pressure than the “high pressure” side of the system) is allowed to flow through the valve and exhaust through the SMTV-3 safety valve, venting the accumulators and rendering the system totally safe.

NOTE:  Sometimes, when there is still pressure on the CO2 tank side of the switch the tank will be difficult to remove from the regulator.  If (when) this occurs just shut OFF the knob to the CO2 tank, then cycle the SMTV-3 safety valve ON then OFF a few times, allowing the accumulators to refill.  There is not much volume of CO2 in the lines so it won’t take long, or very many cycles.  Leave the switch in each position for 4 or 5 seconds.  You shouldn’t hear any hissing as the accumulators try to fill, after the first cycle.

WARNING:  Always point the cannon in a safe direction when test firing them, making sure they won’t fire before removing the tank from the system.

Figure 2 shows the gas flow through the system with the SMTV3 safety valve turned OFF.  Arrows show the direction of gas flow as gas dumps from the system.

Figure 2.
CO2 Delivery System Schematic (Safe Mode).

NOTE:  Pay attention to the direction of the check valves, as indicated by the arrow on the side of the valve.  It is important to note that, if the check valves are installed backwards the system will still function, but the adjustable regulators would have no effect, and the cannon would be firing at full line pressure of the main regulator.   Double check the systems that you have plumbed up.

7.  15002-2 (Clippard) “L” fitting, quantity depends on various aspects of the system configuration including number of guns, locations of guns and other components, and space constraints dictated by the hull and construction.  Phil’s design calls for 7 per (3-cannon) system, but this number may be higher in some cases.

8.  15002-4 (Clippard) “T” fitting,  quantity depends on various aspects of the system configuration including number of guns, locations of guns and other components, and space constraints dictated by the hull and construction.  Phil’s design calls for 5 per (3-cannon) system, but this number may be higher in some cases.

9.  15002-3 (Clippard) “X” fitting,  quantity depends on various aspects of the system configuration including number of guns, locations of guns and other components, and space constraints dictated by the hull and construction.  Phil’s design calls for 5 per (3-cannon) system, but this number may be higher in some cases.

10.  MPA-7 (Clippard) actuator, part of each cannon.  The actuator is powered by high pressure CO2, and opens the cannon’s ball valve to dump low pressure CO2 out of the cannon’s accumulator, through the manifold and breech, where it picks up the bearing(s), then out through the barrel(s).

NOTE:  One or more metal spacers (washers) will be installed between the MPA-7 and the cannon ball valve.  These spacers are essential to cannon performance. If the MPA-7 actuator is removed from the cannon be sure to keep the same MPA-7 and spacers with each cannon.  It is common for the internal plunger of the MPA-7s to be modified for a particular cannon, and they ARE NOT interchangeable between cannon.  If the MPA-7 actuators were removed and reinstalled and the cannon “hisses” CO2 out the barrels, or fires with noticeably low power, this means the incorrect number of spacers was installed, or the incorrect MPA-7 for the particular cannon was installed.

CAUTION:  Readjusting the MPA-7 and spacers is a fairly simple operation once you have done it once, but can be very aggravating the first time you try it.  Ask for help before you damage your cannon – the plastic screw threads on the ball valve are easy to damage.

11.  Accumulator, part of each cannon.  The accumulator stores low pressure CO2, which is used to actually propel the ball bearing(s) out of the barrels when the MPA-7 actuator is activated.

12.  Servo wheel or arm, possibly modified, quantity as needed depending on the number of guns to be fired.  One servo (one radio channel) can easily be set to fire two different guns (or pairs of guns simultaneously).  Mount the servo with an arm or cut-away wheel so that in the center position, no SMAV-3 valves are pressed, but moving the servo to either end of its rotation will press one or the other of the SMAV-3 valves, firing the connected gun(s).

13.  3814-7 (Clippard) urethane tubing, used to connect the various components of the system together and deliver gas to cannons.  Do not attempt to cut corners by using a vinyl or nylon hose that is not rated for the pressures and temperatures that this tubing is rated at!  This tubing is available in several colors – use one color for your high pressure lines, and a different color for low pressure!  Figure 1 shows different colors for high and low pressure, and any easily recognized combination will do – I use gray for high pressure and white for low pressure, simply because I have a lot of both laying around.  Try to avoid using the same colors as the insulation in your electrical system’s wiring, so it’s easy to tell at a glance what everything is for in your ship.

14.  (not shown) 5000-4 (Clippard) hose clamps, quantity depending on system configuration.  Hose clamps slip over the ends of tubing sections, where the tubing is pressed over barb fittings, to help keep the tubing secure.  Phil’s design calls for 51 clamps, however some systems may require more.  This is a good part to keep extras of in your parts kit.

15.  (not shown)  15004 (Clippard) female-female 10-32 hex couplers.  Phil’s design calls for 7 of these couplers, to connect various other fittings to one another.  Individual systems’ usage of this part may vary, but this is another good part to keep extras of in your parts kit.

16.  (not shown) 11752-2 10-32 x 1/16″ hose connectors.  Phil’s design calls for 42, however this number may vary depending on ships’ configurations.

17.  (not shown) 11999 (Clippard) short coupler (male/male).  Not explicitly called for in Phil’s design, but useful for miscellaneous coupling needs that may be required by some systems.

18.  (not shown)  15006-1 (Clippard) 1/8-27 NPT pipe to 10-32 adapter, 1 per cannon.  This adapter is used to adapt the cannons’ MPA-7 actuators’ 1/8 input port to the 10-32 fittings used elsewhere in the system.

19. (not shown) 15040 (Clippard) swivel fitting.  Phil’s design lists 4 of these as optional equipment.  Swivel fittings may have use in confined spaces, or to allow components to be attached without twisting hoses.

CAUTION:  15040 swivel fittings are not intended for rotating applications.  These fittings will leak some gas, hissing noticeably.  In a ship with a large tank, his may not be a problem, but smaller ships may not be able to afford the CO2 loss.

20.  (not shown) MQC-V3 (Clippard) valve body, used as the male part of a quick-disconnect fitting pair.  Phil’s design lists 4 quick-disconnects as optional equipment, and they can be useful in allowing you to remove elements of the system for maintenance.  Also, a quick-disconnect on the “system” side (i.e., opposite from the tank/regulator) of the SMTV-3 safety switch could provide a convenient point for a club Technical Officer or Safety Officer to connect a temporary gauge, for pressure checks.

21.  (not shown) MQC-F2 (Clippard) 1/16″ hose connector, used as the female part of a quick-disconnect fitting pair.  Quantity is 1 per MQC-V3 used.

NOTE:  The Clippard MQC quick disconnects are notorious for “leaking” slightly after very little usage.  In a large ship with an abundant supply of CO2 this is typically not a problem unless the ship is expected to have a long linger time before or during battles.  However, in smaller ships with limited CO2 this leakage will cause the ship to run out of CO2 prematurely in combat.  A symptom of leaking CO2 is a frozen CO2 tank.

22.  (not shown) 11761-2 (Clippard) Buna-N gaskets.  Although each component comes with a gasket for each port, you can never have too many in your parts kit.  Extra gaskets can be stacked, so that fittings align the way you want them to, or add 11761-1 lead gaskets to the stack.  Be careful not to over tighten fittings, as this will squish the gasket and can cause leaks.  Fittings should be finger tight.

23.  (not shown) 11761-1 (Clippard) lead gaskets.  These can be very useful to place over fitting threads as spacers, so that fittings line up correctly when tightened.

24.  (not shown) 11755 (Clippard) screw plug, 10-32.  These can be used to block off unused ports, to let you turn “T”s into “L”s, “X”s into “T”s or “L”s, etc., and are handy to have in the parts kit.

25.  (not shown) Loctite thread sealer.  Use Loctite on all threaded connections, in addition to gaskets!

CAUTION:  Be careful not to over apply Loctite.  Excess Loctite can plug fittings, making for a very difficult to resolve problem.

Assembly Considerations

  • Mount the CO2 tank with its axis parallel to the axis of the ship hull, with the regulator toward the bow, and raised up.  This orientation will cause weight to be reduced from the forward end of the ship, as CO2 is consumed, allowing the bow to raise in the water slightly.
  • Multiple regulators with check valves can be mounted in an assembly as shown in Figure 3.  A 3-regulator (3-cannon) system would use 3 MAR-1 regulators (Item 4), 3 11752-3 “X” fittings (Item 9), 3 11752-2 “T” fittings (Item 8), 4 11999 male/male short couplers (Item17), 2 15004 female/female hex connectors (Item 15), 1 10-32 screw plug (Item 24), and 10 11752-2 10-32 x 1/16″ hose fittings (Item 16).  A thin plywood panel adds extra stability and convenience – the MAR-1 regulators are designed to be panel mounted.  Drill 7/16″ holes on 1-1/8″ centers.  Connect a short section of 3814-7 tubing (Item 13) from the bottom (source) end of each MAR-1 regulator, to the check valve for each regulator.  The “upper” hose barb is then connected to each cannon’s accumulator using 3814-7 tubing.

Figure 3.
MAR-1 Regulator “Rack”, Front and Side Views.

    • As gas is released from the system (by firing cannons, or even through leakage), significant cooling occurs.  This cooling can become extreme, to the point of frost condensing on the surfaces of the tank, hoses, and fittings in the system.  Frost can clog MAR-1 adjustable regulators, hoses, or it can collect on and in the SMTV-3 safety valve, making it difficult to turn it to the “SAFE” position – it is even possible to break the toggle off the switch, making it impossible to disarm the system safely.  This problem can be relieved by creating a heat exchanger that “warms” the gas with pond water.  Between the high pressure regulator and the SMTV-3 safety valve, run a loop of copper tubing outside the hull below the water line.  The denser water will tranfer more heat to the tubing than air can, warming the CO2 enough to prevent frosting.

Use 1/8″ copper tubing, with an appropriate fitting soldered to either end.  Length depends on the ship layout – about 12″ is needed to make contact with the water, outside the hull.  Properly installed below the water line, the copper is not visible and does not detract from the scale appearance or the operation of the ship.