Although slightly different in operation on both manual or semi auto systems the end result is pretty much the same…
So we will address the manual first.
Firstly a 100mm stainless steel 2 contact, Contact Alarm Gauge can be fitted to the high pressure port on the Manual regulator. This can be wired back to a Visual and audible gas alarm unit.
On inert gases a cylinder/MCP pressure of 200 bar (approx can vary) indicates a full cylinder, so if a setting on the Contact alarm gauge was set at say 50bar and say 20 bar … then the two stages of alarm on the visual and audible panel would be indication that the cylinder was starting to empty (50 bar) and was now about to run out (20 bar) by which time the operator could switch off the empty cylinder and switch on the full one.. and then replenish the “empty cylinder” to once again have one in reserve, he would have time to this, but MUST respond to activate the changeover.
On an Auto system the set up is similar however the low pressure setting is slightly higher… again we have two stages of alarm, however the main difference here is that if the duty side runs out the reserve side will take over and the empty side can be replenished as required. The downside here is as the operator does not have to go to the manifold it can be left and when the unit standby side runs out the system is down.
You could say that the manual setup is an “active” setup and the Auto system is a “passive” set up for the initial cylinder change.
The point of advantage could be convincingly argued both ways. However consider this: on either system an operator has to change a cylinder… assuming, worst case scenario, that he does not respond to alarms, to the point of the process running out of gas…
On a manual system when the “process” runs out of gas the reserve can be engaged immediately by opening a valve. On the Auto system at that stage the reserve is also empty, so a cylinder/MCP has to be changed.