![Image](http://img25.imageshack.us/img25/7785/sketch1j.png)
![Image](http://img25.imageshack.us/img25/sketch1j.png/1/w720.png)
I have finished building the engine, and the valve system is as follows. There is one pressure chamber which feeds all four cylinders, and is itself fed from a CO2 tank. At the base of each cylinder, gas flow is blocked by a fairly standard piston valve inside a Tee. The piston has a return spring to help it close against the cylinder end. There is no pilot valve, but instead the mechanical force of the returning piston is used to push on the piston face and force it open:
![Image](http://img21.imageshack.us/img21/6233/sketch2w.png)
![Image](http://img21.imageshack.us/img21/sketch2w.png/1/w720.png)
As the piston returns down the cylinder, the red rod, which is attached to the piston head but not the valve piston, pushes the valve piston back against the spring and greater pressure on the rear of it, allowing air to flow into the cylinder and drive the piston head forward again.
The problem I have is that I’m not sure how far back to have the piston head go. This is because the valve system presents the difficulty of cutting off the flow of gas into the cylinder as soon as the piston moves forward a little bit:
![Image](http://img194.imageshack.us/img194/2497/sketch3.png)
![Image](http://img194.imageshack.us/img194/sketch3.png/1/w720.png)
Then ->
![Image](http://img34.imageshack.us/img34/1852/sketch4.png)
![Image](http://img34.imageshack.us/img34/sketch4.png/1/w720.png)
So basically only the air that makes it into the cylinder before the piston moves enough to close the valve will be available to propel the piston the rest of the way down the cylinder. My dilemma is that if I have the piston return only say halfway down the cylinder, leaving plenty of available space to fill with air before it moves, the piston stroke is shortened, whereas if I have it return all the way, there is no room for air to enter and there will not be enough air to drive the piston properly once the valve closes.
![Image](http://img34.imageshack.us/img34/2802/sketch5.png)
![Image](http://img34.imageshack.us/img34/sketch5.png/1/w720.png)
So generally I’m just asking for thoughts/advice on how to design the system. The engine, valves, and cylinders is already built, the crankshaft and pistons is not. The dimensions of the engine are (all Sch40 PVC)
Valve Tee: ¾”
Piston Seat: ½”
Cylinders: 1.25” (cylinder diameter must be greater than seat diameter to ensure that the stroke of one cylinder provides enough force to open the piston valve in the next cylinder, with the force being transmitted between pistons through the crankshaft)
Cylinder length: 11”
Chamber volume: 26.6 in^3 or 59” of ¾” pipe (somewhat irrelevant since nowhere near all the CO2 is vented into the cylinder on each firing, but here it is anyway)
Thanks in advance!