Zaphod, relax just a bit here. I am not saying silicone filled piston regs are any less messy to service, I just said they work well when properly packed. I don't make a practice of implying anything, I usually just come right out and say it.
But for the sake of argument, with a good boot, very little silicone oozes out of a piston reg - about the same as will oooze out of a diaphragm reg on a hot day. Admittedly many piston regs have no boot or a poor boot design leading to the general condemnation of the whole breed. SP got it right with the last and very excellent version of the SPEC boots used on the late production Mk 15's and early Mk 20's - right before they threw the whole idea out in favor of their less than perfect TIS system.
In my opinion, a diaphragm reg is more at risk of freezing if some silicone or alcohol is lost as any water that enters the ambient chamber is better able to transit through the liquid to the important parts and cause problems than in a piston reg. In a properly packed piston reg's ambient chamber, silicone is lost form the outside and the internal parts are still fairly well protected.
The problem with many diaphragm designs and flow rates and responsiveness has little to do with the weight of the moving parts but has everything to do with the working range between the hard and soft seats. There is a just a limited amount of air that can be squeezed through that space which limits the flow rate. And unless there is ample internal volume in the IP spaces in a diaphragm reg to provide an adequate reserve until the airflow can get up to speed, the IP will drop substantially with a heavy inhalation at depth.
Dry systems are nice, but on a piston reg it kind of goes against the grain in that the virtue of a piston design is simplicity.
The MK 25 does have a higher parts count than most piston regs but the piston is still the only moving part and there are still only 2 dynamic o-rings in the whole thing (3 if you count the backup o-ring on the piston head). The fact that it uses an HP bushing system and has a swivel, extra ports, trim pieces, etc. does not change the fact that it is still a very simple mechanical design.
But for the sake of argument, with a good boot, very little silicone oozes out of a piston reg - about the same as will oooze out of a diaphragm reg on a hot day. Admittedly many piston regs have no boot or a poor boot design leading to the general condemnation of the whole breed. SP got it right with the last and very excellent version of the SPEC boots used on the late production Mk 15's and early Mk 20's - right before they threw the whole idea out in favor of their less than perfect TIS system.
In my opinion, a diaphragm reg is more at risk of freezing if some silicone or alcohol is lost as any water that enters the ambient chamber is better able to transit through the liquid to the important parts and cause problems than in a piston reg. In a properly packed piston reg's ambient chamber, silicone is lost form the outside and the internal parts are still fairly well protected.
The problem with many diaphragm designs and flow rates and responsiveness has little to do with the weight of the moving parts but has everything to do with the working range between the hard and soft seats. There is a just a limited amount of air that can be squeezed through that space which limits the flow rate. And unless there is ample internal volume in the IP spaces in a diaphragm reg to provide an adequate reserve until the airflow can get up to speed, the IP will drop substantially with a heavy inhalation at depth.
Dry systems are nice, but on a piston reg it kind of goes against the grain in that the virtue of a piston design is simplicity.
The MK 25 does have a higher parts count than most piston regs but the piston is still the only moving part and there are still only 2 dynamic o-rings in the whole thing (3 if you count the backup o-ring on the piston head). The fact that it uses an HP bushing system and has a swivel, extra ports, trim pieces, etc. does not change the fact that it is still a very simple mechanical design.
