Introduction: Simple Set-mounted PVC Blood Cannon for Theatre Special Effects

By
About: Jack of all trades, master of a couple. Eclectic interests combined with a short attention span make me just knowledgeable enough to be really dangerous.

Sometimes when you're doing a  play, killing a few people onstage just isn't enough. Sometimes you need a bloodbath. That was the case for a production I worked on recently. The show opened with the brutal murder of an entire wedding party, and that was just the Prologue. Throughout the play, the violence kept escalating until the final scene, when three characters mow down an entire dance club full of people in the course of a few seconds.
For this scene, I needed to provide something special, a veritable orgy of bloodshed, or the scene would just be anti-climactic.
Unfortunately, by this point in the show I had already used up most of the squibs I had been able to afford to make (see here and here for two different squib designs). Also, my feedback from the Director had typically sounded something like "Blood on the walls! Blood on the floor! Blood on the audience! Blood EVERYWHERE!". Have I mentioned yet how much fun I had working on this show?
In any case, since I had already tied up most of the effects budget in squibs and gallons of blood, I needed to come up with a way to sling tons of blood around, and I needed to do it on the cheap. Here's what I came up with.

Step 1: You Will Need:

Materials:
2-3 feet of 1/2" schedule 40 PVC pipe - rated for 600 psi*
One 1/2" PVC tee fitting - threaded in the center hole, slip-fit in the side holes
One 1/2" PVC bushing - threaded one side, slip-fit on the other
One 1/2" PVC threaded cap
One 1/2" PVC slip-fit plug
One threaded nylon 1/2" hose barb fitting - straight or 90 degree elbow
Three 1/2" 90 degree PVC elbows OR two 90 degree elbows and one 45 degree elbow
Five feet or so of 1/2" vinyl tubing (length will vary depending on where you mount the cannon)
Small hose clamp (optional - not pictured)

Tools:
Air compressor or other source of regulated compressed air (not pictured)
Compressor Hose
One blower nozzle with coupler
One blower nozzle hose barb adapter**
One blower nozzle hose barb**
Drill
Saw
Assortment of drill bits
Pliers
Wrench

Supplies: (not pictured)
PVC primer***
PVC cement***

* We're not going to get anywhere near 600 psi, but why take chances? Exploding PVC can create shrapnel that will kill you. Use the good stuff.
** Usually found packaged together with a few other blower accessories - about $3.00 at Lowe's
*** IMPORTANT - all slip PVC connections in this project must be secured with PVC primer and cement. The cannons build up a lot of back pressure when fired, and any uncemented connections will result in PVC fittings being flung across the stage at dangerous velocities.

Step 2: Cut Your PVC and Assemble the Main Body of the Cannon

Decide where and how you are going to mount your cannon when it's done, and where it will be operated from. You will be making several decisions regarding the size and configuration of your cannon based upon where it will be mounted, as it is much easier to build the cannon to fit the space than it is to modify it to fit after the fact. See Step 11 - A Few Words About Mounting, Placement, Targets and Making It Work for some useful information on this topic.

Using a saw, cut your PVC pipe into 2 longish pipe sections for the main body of the cannon(about 11 inches is a good measurement if space is not an issue- actual length will vary according to where you plan on mounting your cannons. Measure your available space first to make sure your cannons are not too tall) and 2 short pipe sections (about 1 1/2" - used to join fittings together closely). The two longer pipes serve as the reservoir for the stage blood, so the longer they are, the more blood you can load. More is not always better, but give yourself the option if you can. For our show, we found that two ounces of blood was optimal for our needs. Your mileage may vary.

Using PVC Primer and PVC Cement according to the package instructions, join the two long pipe sections, one short pipe section, two 90 degree elbows and one tee fitting as shown in the photo below.
Be sure that the two long sections are parallel to each other. The easy way to do this is to attach an elbow to each long piece first, and then join the two elbows together with a short piece. This makes it easier to adjust the angle quickly before the cement dries.
Top one long pipe with the tee fitting using primer and cement. Make sure that the threaded center opening of the tee faces away from the opposite long pipe, or at least is not facing directly toward it .

Step 3: Prepare the Spray Nozzle

Using a drill, make a small pilot hole (1/8") in the center of the 1/2" plug. Hold the plug with pliers while drilling to avoid making a small pilot hole (1/8") in your hand. We're using fake blood in this project.
Using a 3/16" bit, enlarge the hole you just drilled. This is a good starting size for the nozzle hole. You can always make it larger later if your test runs demand a bigger opening.
Using PVC primer and cement, glue the plug into a 45 or 90 degree elbow, depending upon whether you want to spray blood at an upward angle from your mounting position or not.
Do not cement the nozzle to your cannon yet, unless this particular cannon is a prototype meant for testing purposes, and won't actually be mounted on your stage set.

Step 4: Install the Air Inlet and Screw Cap

Using a wrench, screw the nylon hose barb fitting into the threaded portion of the tee fitting. You can use either a straight barb or a 90 degree barb, depending on whichever works best for your mounting position. It should be snug, but it doesn't have to screw in all the way flush to the tee fitting.
Take the second short pipe, and cement it into the top of the tee fitting.
Cement the bushing onto the end of the short pipe.
Screw the threaded cap onto the bushing.

Step 5: Install the Air Tube and Mount the Cannon

Here's an easy one: Take one end of a piece of 1/2" vinyl tubing and shove it onto the nylon hose barb until it stops. The length of the tubing will depend on how far away from the cannon your operator will be. Closer is better. For optional added security, secure the tubing to the barb with a small hose clamp.
Mount the cannon in its desired location and run the air tube to the operator's location. See Step 11 - A Few Words About Mounting, Placement, Targets and Making It Work for detailed information regarding choosing your mounting and placement. If you are using multiple cannons, try to consolidate them into as few different operator locations as possible, to reduce the number of air hoses/supply tanks that you will need to power them.

Step 6: Attach the Spray Nozzle

With your cannon mounted in place, slip the spray nozzle onto the long tube and point it where you want the blood to go. It may help to insert a  3 ft. long 1/8" dowel rod or straight piece of wire into the nozzle to help you visualize where the blood spray is aimed.
If you need to, adjust the mounting position and re-aim until you have the nozzle pointed exactly where you want it.
With a marker, draw a register line on both the nozzle and the long pipe to help you line them back up correctly when you cement the nozzle on.
If necessary, unmount the cannon.
Remove the nozzle, apply PVC primer and cement, and cement the nozzle on, aligning the register marks to ensure proper aiming.
Remount the cannon if you had removed it previously.

Step 7: Put Together the Blower Assembly

Screw the Hose Barb Adapter into the Blower Nozzle. Screw the Hose Barb into the Hose Barb Adapter. If the Blower Nozzle does not already have a coupler installed, install one that fits into your Compressor Hose. Use teflon tape on the threads. That is all.

Step 8: Run the Air Supply to the Operator's Location

Attach the compressor hose to the compressor (or other regulated compressed air supply), and run the hose to the operator's location. Attach the other end of the hose to the blower nozzle. Set the regulator to 75 psi and turn on the compressor, if applicable. Otherwise, make sure your air supply is pressurized.
How this actually works will vary according to your choice of air supply. If you are using a large stationary compressor with hard-plumbed air outlets, you should pick the nearest outlet to the operator's location and run the hose from there. If you are using a portable compressor, place it as close as is feasible to the operator's location. Alternately, you may be using portable air tanks, in which case the tank may best be placed right at the operator's location. If you have multiple operator locations, you may want to run the main hose to a central location and install a manifold, then run additional hoses to each operator location.
The important thing is that each operator location has at least one blower nozzle attached to a regulated air source. How you make that happen is ultimately up to you.

Step 9: Load the Cannon

Here's another one that will depend on your mounting and placement choices, but basically you will remove the screw cap, insert a funnel or fill tube into the cannon, pour your desired amount of stage blood into the cannon, and replace the cap.
Fill the cannon to just below the tee connector or lower. Overfilling will cause the stage blood to leak into the air tube or out of the spray nozzle.
The effect is now ready to operate.

Step 10: Operate the Effect

To operate the effect. the operator inserts the blower nozzle hose barb into the air tube, holds it firmly in place, and squeezes the trigger. Blood flies all over the place, actors drop like flies, and the audience goes "oooh".
You can vary the effect by changing the air pressure, the amount or viscosity of the blood, or the size and shape of the hole in the spray nozzle. Test until it does exactly what you want it to. 75 psi worked for us, but you may need to adjust the pressure up or down.

Step 11: A Few Words About Mounting, Placement, Targets and Making It Work

Every set is different, every show is different, so I can't tell you exactly how to mount your cannons or where to place them for best effect. Here's some information that will help you make that call yourself.

Mounting
1. The cannons should be securely mounted to something solid, whatever that may be. Otherwise they will whip around like a Wacky Water Weasel when you use them. That could be bad.
2. It's not really important how you mount the cannon as long as it's secure. Pipe clips, plumber's strap, zip ties, duct tape - whatever works.
3. The cannon should be mounted as vertically as possible. There's a little bit of wiggle room if you need to adjust the aim a little off from 90 or 45 degrees, but the more you angle the cannon, the less blood it will hold without leaking.
4. Make sure you have enough access to reach the screw cap to reload the cannon. For tight spaces, a funnel with a bit of vinyl tubing stuck onto it can make reloading much simpler. In extremely tight spaces, you may need to skip the screw cap altogether and fill through the spray nozzle using a syringe.

Placement
1. Anywhere with line of sight between the nozzle and the target will work, as long as you can hide or disguise the cannon from the audience.
2. Some ideas: on the back of a flat (with a little hole for the blood to come out), inside a doorframe, on the back of a chair, inside a piece of furniture, disguised as an electrical conduit on the wall or a radiator pipe, inside a hollow book on a bookshelf, disguised as a light switch or electrical outlet, the possibilities are endless.
3. The other main consideration about placement is the length of the air tube. Anything longer than about five feet will start to introduce a noticeable delay in the effect that is only partially correctable by increasing the air pressure. Place the operator as close to the effect as you can. This might mean that the operator will find him/herself in some pretty odd places during the performance, like under the stage or inside a piece of furniture.

Targets
Anything you want to get blood on is a target. For our recent show, the cannons were used to:
a) Simulate gunshot wounds on actors up to 8 feet away from the cannons, by creating a big blood splotch on their chests or backs
b) Simulate bullets to the head by firing a big blob of blood directly at the back of the actors' heads from very close range. It happened so fast that the audience didn't have time to notice that there was no entry wound in the front. The backsplash behind the actors was pretty impressive too.
c) Spray blood onto the walls and floor of the set, just to intensify the carnage. Again, this happened fast enough that the audience wasn't able to register where all the blood was coming from, just that there was suddenly blood all over everything and everybody.

Making It Work
Making the effect, well... effective depends not only upon the cannon itself, but also the coordination of staging, lights, sound effects and the ability of the actors themselves to "sell" the moment.
Here's a little theatre secret for you: The moment that an actor draws a gun onstage, everybody in the audience will be looking at the gun, and they will keep looking at the gun until something big and flashy makes them look elsewhere. Use this to your advantage. Misdirection is your most valuable tool when creating stage illusions.

Step 12: Tweaks and Future Improvements

For a couple of the effects in the show, I had to tweak the design a bit to camouflage the device. We needed to mount two cannons onto a really beautiful black welded steel "throne" made by fellow member RedHandFilms (who also made a very cool blood squirting knife that I hope he will someday do an Instructable for.... You listening, Red?).
The structure of the chair was such that a PVC cannon would stick out like a sore thumb, so I made a modified version using black flexible sprinkler tubing and a black 90 degree elbow zip-tied to the chair frame, so that it looked like part of the chair's structure. The tubing went down through a hole in the stage and looped back up behind a piece of furniture, where it connected via a hose barb to a straight PVC pipe with the screw cap, tee and air tube connections, just like in the regular version. The air tube ran through a hole back under the stage floor to the operator's location. The loop under the stage and back up served as the reservoir usually formed by the two longer PVC pipes in the standard version.

For the future, there are some changes that could be made to improve the device a bit, budget allowing.
One thing that I'd like to try is eliminating the air nozzle/compressor section, and replacing it with one of the many air cannon/potato gun devices that can be found on this very site. If the air cannon is one that uses an electric sprinkler valve, in theory all the cannons could be connected to non-dim circuits in the lighting control system and operated remotely.
I'd also like to look into a check valve/gravity reservoir setup that would allow the cannon to refill itself after firing. Combine this with the potato gun idea, add an air line or tank to automagically repressurize the spudchucker's air chamber after firing, and you get a remotely operated blood cannon that is capable of multiple shots in fairly rapid succession. This would obviously require a bit of R&D, but I think the concept is sound.
Also, while I was buying the sprinkler tubing for abovementioned chair mod, I was intrigued by the variety of sprinkler and fountain heads available. I bet some of those would make excellent blood nozzles for certain applications.

Finally, if anyone uses this system (or has used a similar one) for a show, I'd love to know of any improvements or mods you make. Drop me a line and let me know what you come up with.