Modulator Valves valves are connected using a manifold to construct a set of doubles, or connected together. The manifolded doubles are sometimes disassembled, the manifold removed, and the left-hand & right-hand modular valve manifold ports are plugged to make two single cylinders. Left and right modular valves are also commonly found in the pairs of single cylinders used with fully closed-circuit rebreathers. Its various designs have deliberate incompatibilities to preclude the possibility of errors when handling different types of compressed gases at differing working pressures. The regulator first stage DIN connector is a male screw type, and instead of clamping on to the outside of the valve, it screws directly into the female DIN outlet of the valve. The sealing O-ring is held in the end of the regulator connector rather than in the face of the outlet.