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At 02:30 PM 07/03/97 -0500, you wrote: >Ed, Dave, Ian > >Ed, You wrote: > > >>A negative aspect is that Odin 1st and the 2nd stages are _BOTH_ >>upstream valves. It means if anything goes overpressure they slam >>shut. In contrast downstream regulators would free flow and you could >>still breathe (I new about the 2nd stage and that is probably why George >>trashes it all the time, the 1st stage is news to me). >-------------------------------------------------------------------------- Chkboone reply >As I understand it: > >An up stream valve tends to be shut by pressure from the previous stage, >chamber, or supply and requires mechanical or other force to open it against >this pressure. >In the odin second stage this is a pilot valve that will not allow the flow >of air into the chamber unless it is tilted by mechanical force. The >intermediate pressure from the first stage holds the valve firmly against the >seat otherwise. Ian's comment: correct >A downstream valve tends to be opened by the pressure from the previous >chamber and must be held closed by mechanical pressure so that if the spring >or other device that applies the pressure holding this valve closed breaks or >slips off it's seat or whatever the valve will be forced open by the pressure >from the supply side just as if there is no valve there. Ian's comment: also correct >Looking at the diagrams I have (owners manual) it appears that the 1st stage >is indeed technically an upstream valve because the pressure from the tank >tends to hold the first valve shut until it is opened by the reaction of the >diaphragm to a pressure reduction in the second chamber. A failure of the >diaphragm mechanism will cause the supply from the tank to be shut off by the >force of the pressure from the tank holding the valve against it's seat. >It also appears that the spring behind this valve will act to hold it closed. Ian's comment: poor diagrams I'll explain below >The reason for the pressure relief mechanism in the hose is because anything >that allows the intermediate pressure to get dangerously high would blow the >hose (or the second stage valve mechanism) because the second stage is an >upstream design - not because of any feature of the first stage. Such >causes might include corrosion, spring breakage (behind the first stage valve >seat) . . . . Even a slow leak from the first stage would blow something out. Ian's comment: true >In any case, if a failure in the first stage allowed tank pressures to reach >the output chamber of the first stage, and therefore, the second stage >through the hose you could end up imitating a red dye marker. > >For this reason I don't see how any first stage could ever be downstream in >the same sense as a second stage can. Ian's comment: There are a great many downstream first stages (almost all piston type) which is why the majority of second stages are also down stream. If the 1st stage malfunctions the 2nd stage acts like a safety valve and opens resulting in a free flow. >The normal intermediate pressure on the odin is around 145 psi. - from the >owner's manual ! Ian's comment: my manual states max 152 for the odin/jetstream part # 2960 first stage although I set mine at 140-145 psi because of the cold water around here. (have never had the reg freeze, and I have never used the cold water kit) >------------------------------------ > > To Ian, > > Are my diagrams too simplified ? Am I missing something here? I also do >not see how the first stage is balanced - can you explain further. As I >understand balancing it equalized forces on either side of a valve popet or >diaphragm usually by allowing a passage of gas between opposite sides of the >device. I can't see a path here but, again, my drawings may be >oversimplified. Or I may not understand balancing. >Chuck Chuck: you seem to understand the concept well, unfortunately the diagrams are not very good and there is no description in the manual. First, think of the airflow as a river. Most US made regulators have a Fixed cone in the current, sort of a dam. If the cone faces downstream, and the seat is pushed up against it by a spring, it is a downstream unit. If the cone faces towards the current and the seat is held off by a spring, it is an upstream unit. (the old Dacor 200 is the only up stream first stage I can think of). Typically down stream units got harder to breath as the tank pressure dropped and upstream units got easier. The intermediate pressures would very as much as 25 psi between 3000 and 500 psi. With balanced diaphragm first stages, they look very similar to the upstream unit but there are a couple of very important differences. The assembly on the high pressure side of the dam is hollow, with one side of it fitted into an o ring sealed balance chamber. The pressure from the intermediate side flows down through the seat/cone mechanism into the balance chamber and this in essence suspends the unit between two equal pressures. In theory the will be no change in intermediate pressure until the tank pressure drops below the set IP (140-150). In reality the IP will change less than 6 psi with a tank pressure change from 3000 to 500. The odin works on the above concept with the only exception being that the cone (called valve piston in the manual) moves and the seat is fixed as part of the dam. The regulator will work even with the balancing spring removed (I tied it once just to see)and the IP will creep up if there is a problem with the cone, seat or balance chamber o ring. The only way that the regulator first stage could lock up, would be if some contaminant were to block the passage in the hallow valve piston. Is is extremely unlikely as the filter would block anything coming in and there are no internal plated parts to flake etc. If this passage were plugged, you would have a true upstream unit. USD, Dacor and Mares balanced diaphragm units use this same principle. Hopefully, what I have written above makes sense to you, it's easier to understand when you have a torn down reg or good diagrams in front of you. If your still lost, let me know and I can probably come up with a diagram or two that I could fax you or given time put on my web site or e-mail. Ian marshall@va*.co* <http://www.vaxxine.com/advtech> -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send list subscription requests to `techdiver-request@aquanaut.com'.
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