Basic selfbondage techniques and devices
Pneumatic Release
By Riddle


Originally posted in the forum:
(Please look there for even more information and warnings on this subject.)

Safety is always paramount in an daily life. Self bondage requires even more attention to detail to ensure safety. Some bondage release setups have bothered me in the past and I am constantly seeking a safer and more secure method to time the release.
This search brought me to this forum and to study pneumatics. Keys magnetize, temperatures vary, and strings tangle. Compressed air can provide much more holding power than an electric magnet, without the concern of electric wires attached to your bondage setup. Compressed air may provide hundreds of pounds of pushing or pulling power with a fairly small cylinder. This force must never push or pull on the restraints or anything else attached to the body. Safety is my highest priority.
By replacing the electric magnet on the self-bondage stocks with an air cylinder moving a pin, the holding power can be increased substantially. Then again, I do not want to spend $100 on a magnet that may not hold well enough. By using an industrial air cylinder on each wrist cuff, I have increased the redundancy to double. The 3/4 inch bore X 1 inch stroke air cylinders at the local industrial supply company cost me about $15 a piece. The single acting ,spring loaded return ones are the cheapest and safest in my opinion. These require air pressure to continue holding and return back when the air pressure is gone. Double acting cylinders require air pressure to move in either direction. The most common failure in industrial applications is air leaks. This will at least reduce the strength or cause complete lack of function, depending upon the rate of air loss. Only in extreme cases under severe conditions will a lack of imaintenance cause the cylinder to seize up. For bondage applications, careful inspection and lubrication will ensure this will not happen. Then again, I will not ever see my cylinders reach over 100,000 cycles while exposed to constant industrial dirt and grime. My home is cleaner than that.
I have no intention of building the electric stocks as shown on the main page. My intended application is in both a wooden cross format and a medical 6 point bed tie down setup. My wrist restraints are locking medical restraints which require the other hand to unlock and release. Due to this limit, I desire a release mechanism that lets go of the restraint instead of the key. An electric magnet capable of holding is well beyond my budget. Then again, a magnet requires a metal plate to hold. This is often heavy, gets warm, and shall never be above my head. With the cylinder operating a moving pin to catch the tie down ring on my wrist restraints, the release should be extremely reliable and only be holding the weight of my restraints. So far, this sounds safer to me.
By using air pressure to hold, I am hoping to build a setup with sufficient redundancy to prevent another scare. With multiple timers controlling multiple electric controlled air valves, the release should occur at the programmed time. All air valves will be wired and plumbed to dump the air pressure when they lose electricity. In the event of a power outage, I will be instantly released. The electric valves that I chose have 12 volt coils. This allows me to power the relays from an exhaustible power source (batteries). The timers will be plugged into the wall but will only control more relays in line with the battery power. The air compressor will never be directly attached to the bondage setup. I desire to use a small portable air tank to supply the initial pressure, By intentionally installing a small air leak, the pressure will not last forever as a final fail safe.
Each of the air components were selected by air pressure rating to ensure safety. My air compressor shuts off at 100 PSI. Therefore, anything rated above that in industrial applications is safe. The valves are rated at 125 PSI. The fittings are 160 PSI. The hose is 250 PSI (this is the most critical in an air system). The air cylinders are rated at 300 PSI.

My parts order was at the store today! Both air valves and air cylinders are in my possession and tested. The function is good, but the air cylinders are noisy in operation. The finished product will be cushioned with rubber grommets to reduce noise.
The following images are the actual parts that will be used.
This is the electric air valves (solenoid air valves). The pair are bolted together and connected to a compressed air supply. The upper connection is normally closed and the lower one is normally open. The brass item installed in the lower port is an air exhaust muffler.
Now comes the fun part, building the brackets to hold the air cylinder and sliding pin.

Here is pictures of the build process and the completed prototype (prototype as in work in progress). At this time, I have not connected the air lines or set up the controls. The plastic lines with duct tape on the ends is there to keep the air cylinders free from debris during the contruction and will remain as long as the air lines are not connected. Until the sawhorse is comfortable and safe, the controls are not needed.
Click on the pictures for a larger view.
Here is a picture of the rough draft of the cylinder and 4 inch sliding latch inlaid into a 2x4. In the background is the other cylinder and latch connected together. The piece of wood over the cylinder is bolted to the air cylinder mounting bracket. This was replaced with a 3/16 thick steel plate in later designs.
The latches have notches on one side. When installed into the 2x4, the latch should never be able to turn into the notch because of the tight fit of the groove cut into the board. I used a 3/16 thick piece of steel about 1/2 inch wide by 4 inch long. On the cylinder end, I drilled a hole the correct size for the pin on clevis (the end of the piston rod). The other end of the steel was drilled with a 3/16 inch hole and notched on one side to barely fit over the latch handle at the skinny portion. The notch in the steel is opposite the notches in the latch to prevent it from disconnecting or jamming. The groove in the wood is also a close fit for the steel bar.
Notice that the latches will be mounted upside down in the finished product. This is why I will not use this design for any bondage that could place my full weight upon the latch. If the sliding bolt is partially pulled out, it may jam and fail to release.
Here is the next 2x4 already drilled out to begin carving out the space for the air cylinder and latch. After this point, all further wood removal was by hand with chisels. The holes were drilled with spade wood drill bits. This type of drill bit leaves a fairly smooth and flat bottom except for the center point but does not work well when re-drilling holes bigger.
Here is the the second draft of the inlaid parts. After the groove was cleared out, another hole was drilled from the air cylinder end of the board large enough for the air cylinder to enter, thus allowing a shorter groove, easy air line connection, and extra wood above the air cylinder. Minimal wood was removed to prevent the board from breaking. Most of the air cylinder is to the right of the piece of wood in this image. The groove for the steel connecting bar is as long as possible and a close fit to prevent problems. In this image, you can see the rubber bumpstops. On the piston rod just to the left of the piece of wood is a black rubber grommet. This prevents the cylinder from traveling all of the way back and cushions the stop. At the far left end of the latch groove is a clear plactic bumper for the latch bolt to strike. Fully piston travel is unavailable in this direction also. These cushions quiet operation and extends cylinder life (the cylinder is not pounding itself to death).
Here is the first picture of real progress! The middle board is the rough draft. Above and below it are 2 finished, functional air controlled bondage latches. The upper latch has a medical restraint cuff sitting in place ready to work. As you can see, the groove is covered by a 3/16 steel plate held in place by 8 countersunk wood screws (gold color). The 2 zinc plated countersunk screws hold the air cylinder in place. (sorry, my soda reserve also appears in the photo.)
Here is what not to do! When using countersunk wood screws, one must be very careful to prevent splitting the wood. All screw holes were pre-drilled and countersunk to prevent wood splitting. One good trigger pull on my corded drill sent the screw too deep and caused this split. The screws should be installed either by hand or with a variable clutch drill. Without the clutch, it is very easy to ruin pieces. I have several split boards that must be replaced.
Here is the arm rests installed on the wooden saw horse. Notice that they are perpendicular to the legs instead of parallel to the ground. This is extremely awkward and uncomfortable. To bad all 4 rests must be completely redone to fix this error. When the rests are leveled, the split boards will be replaced.
How does this look? Pardon the clutter, I have limited space and did most of the work in my living room. The leg restraints are held in place semi-permanently by a piece of wood going through the d-ring and screwed into the 2x4. No need to lock these since no one will be reaching them and leaving early.
This project was built using regular 2x4 lumber and basic tools. One power tools was required and two others were a big help. A 3/8 inch drill with variable trigger was invaluable for this project. The 7.25 inch circular saw (skill saw) and electric palm sander were very helpful and saved much time. The wood used for this project was scraps that I had laying around. A set of regular drill bits, spade wood bits, wood chisels, one countersink bit, and some screw drivers complete the tool listing. The metal plates could be purchased from a metal supply store already cut to size. With either sand paper or a metal file, the plates can be smoothed up nicely. The bevel on the plates was done with a file and some patience. A disc grinder would make the bevel faster to make, but would still require a fair amount of smoothing. The steel connecting bars could be made from 3/16 bar stock 1//2 inch wide. Dimensions may be modified depending upon local availability. Just don't go too thin.

Here is my final update for this thread. The project works very well. It may even be considered too good for some SB enthusiasts. Once everything is in set up and the bondage starts, there is no option for second thoughts. This setup will hold for the set time: no more, nor any less. This design has no mercy for those who set the timer too long. You will be securely bound for the entire session.
Before trying any actual bondage with this setup, I intentionally tried to break the latches with my dominate hand. By only using one restraint cuff fastened but not locked, the latch was tested for weakness. I did not have the strength to pull the latch pin out of its mounting bracket. It is strong enough to not even allow me to pull the pin up enough to jam the mechanism. It simply held. If I was using this latch on a bondage cross or post, my full body weight on a single latch may be enough to wedge the latch pin into its mounting bracket. Therefore, this design shall remain solely for installation into an arm rest for either a bondage chair or sawhorse. By staying within these boundaries, my self bondage sessions should remain safe enough for years to come.
Here is some pictures of the final design for your information. Clicking on the picture will bring up a larger image.
Here is the electric relay to control the wall power with batteries. The grey box is a home electric outlet box with a blank cover. On the side is a 120 volt coil relay from Radio Shack installed into a mounting bracket. The mounting bracket is installed into a carefully cut hole in the side of the box. All wires are soldered onto the mounting bracket electric tabs. The relay simply plugs into the mounting bracket to connect all of the wires. By using this method, the relay is easily removed or replaced as needed without concerns of disconnecting any wires. When the coil is energized by the electric timers, the battery wires are connected to the black wire leaving the box. With this method, only 12 volts from AA batteries is ever connected to the actual bondage furniture.
Here is a picture of my timers connected to an power strip. Yes, there is 3 digital timers used. You cannot be too careful with bondage. The first timer (closest to the power strip) has its outlet opposite the input. It is a weekly timer with up to 20 separate on/off times. I only have one off time set into this timer for every day of the week. This way, it will always turn off today. The other 2 timers are only daily timers with up to 6 on/off times. They are supposed to have watch batteries installed to keep the time and timer routine stored. The batteries are normally removed. This way, once they lose their power input, they will never turn on without my intervention. The default mode for these timers is off.
The timing setup for the bondage setup is simple. The first timer is set to turn off a while after the desired end time (30 minutes or so). After setting its off time, I manually turn on its output to set the next timer. The second timer is set either close to or right at the desired end time. Once it is set, I turn on its output and set the final timer. The final timer is set with both an on and off time. The on time gives me time to get into position before the latches slam shut. The off time is set for the desired release time. This allows for a very precise bondage time.
Here is another electrical box installed at the end of the lower center 2x4. This contains a switch, circuit breaker, and electrical connection strip. By having a switch on the bondage furniture, I can cycle the valves multiple times to verify proper operation of the air valves, cylinders, and latches quick and easy. Due to its mounting location, I cannot operate the switch while in bondage. The wiring setup requires the switch to be in the “on” position before bondage can start. If I need to perform a last minute abort before both hands are held down, I have that option.
Here is a picture from the foot end of the sawhorse. From this fuzzy (sorry about the quality) image, you can see the air valves bolted into place, the air lines going from the valves to the input connector, and the wires from the valves to the connection box. The wires were wrapped with plastic spiral wrap to prevent them from damage and held in place with plastic cable clamps. The brass item above the grey box is the compressed air input connection. I used industrial quick connections on the supply line, air tank, and air hose. For a slow air leak, the brass fitting is not tightened all of the way. The air leak is extremely slow, but will eventually allow me to be released if all else fails. The fitting is screwed in enough to prevent it from unscrewing. The sawhorse leg protects me from this leaking connection both from the possible chill of the air leak, and from the hose if it came loose. The air lines on this side are also held in place with cable clamps.
Here is a better view of the air lines and valves. Notice that the air valve inputs and outputs are connected to a common line. This means that both valves use the same air supply and must work together to hold me bound. If the valves are ever in different positions, the supply line gets connected to an exhaust port and is quickly dumped. This ensures that if one of the valves fails to function, I will be released.
Here is another picture of the air lines. In this photo, you can see how the air lines are connected to the arm rests. Notice the short lines. If one of these comes loose, I should not get hit with the air line. The air released may chill me some, but there is not enough compressed air to cause frostbite. The air cylinders only require 0.88 cubic inches of compressed air for full movement. Therefore, very little air comes out of the exhaust ports under normal conditions. I put my hand on the mufflers and cycled the valves a few time to feel the output. The output was barely noticeable at that distance.
This picture is the new top board on the sawhorse with a variety of metal rings beside my locking wrist cuffs. All of these hardware items except for the green clips fit into the latches. With this design, you could use the latch on rope, chain, wrist cuffs, or anything else that could be attached to one of those hardware items. You are not required to go out and purchase an expensive set of wrist cuffs. The latch could easily be used to replace the electric magnet in the SB wrist stocks described elsewhere on this website.
In this image, you can see the arm rest with a metal chain link resting in the cutout slot without the latch activated.
In this image, you can see the arm rest with a metal chain link resting in the cutout slot with the latch activated. Notice the pin goes all the way to the plastic bumpstop.
This image shows the tank connected to the sawhorse. The yellow coils is the air line. Between the air line and tank is a pressure regulator and air filter. It connects to both the tank and air line with quick release couplers of the same type as used elsewhere. The pressure regulator is set at 60 PSI, a reasonable pressure. This is set just high enough to allow the valves and cylinders to function quickly, but not so much that the cylinders have full force. At this pressure, the entire sawhorse shakes when the pistons move. Anything more is overkill. The tank has 2 couplers and a pressure regulator permanently mounted to the tank for other purposes unrelated to bondage.
Here is both of my portable air tanks with the focus on the larger one. The red tank is 11 gallons (more than I want/need for bondage) with just a quick coupler installed into its tank valve. This would be the preferred setup to connect the regulator and filter to the tank. The black seven gallon tank is from the automotive section at Wal-Mart. These tanks were originally intended to quickly inflate car tires. By replacing the original air hose (which had a permanent tire chuck on one end) with a compressed air fitting, I am able to use them for other purposes. The intended method to fill these tanks is with an air chuck on the valve. You could use the same air source that you use for your car to fill these tanks. A good air compressor would be the best method. The cheap 12 volt tire inflation pumps would burn up before inflating one of these tanks.
After completing the setup and testing it a few times, I have decided that it works very well. This provides strict bondage for the desired time. Due to the unforgiving nature of this bondage setup, I plan to add additional safeguards to the electric controls in the future. In case of emergency, there is no release. I currently have a mechanical thermostat with plans to purchase another. One will be set to either 85 or 90 degrees Fahrenheit. The other will be set to 65-70 degrees. The upper one will release if something causes the temperature in my home to go higher than desired, such as a fire. The lower one will be protection from low temperatures. The only change to the air system that I would like to make in the future is the tank itself. At 1 cubic inch per cycle of the air valves, I have not been able to come anywhere near using the seven gallons available. A much smaller tank permanently mounted to the sawhorse would be more appropriate. I will probably try either 1 ¼ or 2 inch PVC pipe with one end capped and the other connected to the air valves through a ball valve. A 1¼ inch piece of pipe 12 inches long has 14 cubic inches of air volume. This would be plenty for one bondage session. For those without a compressed air source, a cheap bicycle pump capable of 60-70 PSI would work just fine with such a small tank. Even one of the $10 12 volt car tire pumps could handle this as long as the user did not over-inflate the tank.
As previously mentioned, this setup allows for strict bondage. The first session with it was rather uncomfortable. I set the timers for about 45 minutes and had plenty of time to rethink the design of the sawhorse. For padding, I laid a pillow on top of the sawhorse for my chest and face. For the lower torso, several layers of cloth provided the padding. On my knees, I wore a pair of cheap foam knee pads. After the timer latched the wrist restraints, I was stuck. After a few minutes, I realized that no matter how smooth a 2x4 is sanded, one cannot comfortably lay down on one. The next thing that I noticed was the leg and arm rests were too high. To actually lay on the top board, I had to either slide forward or back. This put either my arms or legs at an awkward angle. The next thing discovered was the added pressure on the stomach and bladder. If the stomach is irritated at the start, it will become upset shortly. The bladder should be empty before starting. Nether of these actually caused any issues, but are mentioned so that you are aware. The wrists and ankles could not move the entire time. Any discomfort with the position had to be ignored because there was nothing that I could do about it. My right knee tends to be a little sensitive to constant pressure at this time. During the session, it let me know more knee padding was required. At the end of the session, I was very happy for release.
I made changes to the sawhorse to make it more comfortable before trying again. The biggest change was installing a 2x8 on top of the top 2x4. This not only widened the resting place, but also had the effect of lowering the arm and leg rests. The foam knee pads were replaced with fabric lined knee pads with a hard plastic cup on the bottom. These relieved most of the pressure on my knees by spreading out the pressure. After an initial test fit without the restraints in place, I set the timers for 2 hours and tried again. An hour would have been a better choice. This time, everything went much better, but I did find some room for improvement. The knee pads did not stay in place on the rests because of the plastic bottom. A set of knee pads with the rubber grip surface would have been a better choice, but I did not get them because of the added cost ($25 instead of $10). The thickness of the new knee pads meant that the ankle restraints needed to be raised up to give a more comfortable level position. After a while, I noticed that the insides of my legs were getting sore because of the edge of the top board. I curved the upper edge to roughly a quarter inch radius. Half or one inch would have been much better. The distance between the leg and arm restraints needs to be another inch or 2 for more comfort. Other than these minor irritations, this session went very well. In the future, I may set the timer for longer periods of time after improving the comfort some more. Either that, or make a bondage chair.
At this time, only one question remains. Would you try this?

Originally posted in the forum:
(Please look there for even more information and warnings on this subject.)

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