If you use lithium crystals rather than the specificed di-lithiuim crystals your TX 50 will suffer an anti-matter explosion which will void the warranty - and most life forms in your quadrant.
Bascially, your first stage is a balanced diaphragm design that also has an upstream seat carrier in it. Balancing of the seat carrier ensures that the intermediate pressure of the air sent to the second stage will not vary as the tank supply pressure falls.
In an unbalanced diapghragm first stage the IP would increase as tank pressure falls - but no one makes and unbalanced diaphragm design as it is very simple and inexpensive to balance the seat carrier.
In an unbalanced piston first stage the IP decreases as tank pressure falls, usually by about 15-25 psi as the pressure drops from 3300 to 300 psi. Unbalanced piston first stages are produced as they are very simple, very reliable and have no high pressure air spaces past the seat making them very easy on the dynamic o-rings. Balanced piston first stages are also very common and generally, but not always, have lower parts counts and higher flow rates than diaphragm designs.
When you inhale from a diaphragm first stage, the diaphragm moves inward and presses on pad mounted to a little stem that then lifts the seat off the orifice and allows aior from the tank into the first stage. Whe you stop drawing air from the first stage, the IP increases to the point where it presses the diaphragm back against the mainspring on the other side of the diaphragm (which is what determines the IP) and cause the spring on the back of the seat carrier to push the seat carrier back onto the orifice to stop the air flow. Ambient pressure is also allowed to act on the same side of the diaphragm as the mainspring so the total pressure increases as you go deeper which in turn ensures the IP maintains a constant difference over the ambient pressure. So if you have an IP of 140 psi at the surface, when you are at 132 ft with 4 more atmospheres of pressure you'll have an IP of 199 psi - 59 psi higher than at the surface but still 140 psi over the ambient pressure.
The second stage is also balanced which means there is a hole through the center of the poppet which allows air to flow from inside the orifice through the poppet to a balance chamber that then holds air that will press against the poppet with near equal force in the other direction to balance the force of the air pressing against the seat that is n contact with the orifice. this allows a much lighter spring to be used in the second stage, it also allows a larger orifice to be used and it makes the second stage less sensitive to any change in IP.
For safety purposes "balanced" second stages still have a downstream bias, meaning the area of the poppet in the balance chamber is still slightly smaller than the area of the seat of the poppet in contact with the orifice. This ensures that if the first stage seat fails or leaks causing an excessive IP that the second stage will freeflow and vent the excess pressure before the LP hoses burst.
Hope that helps.
