My reg freeflowed at 80 feet
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Piston regs don't like cold water well. As air expands inside the reg, it causes adiabatic cooling. (Try letting a reg free flow on land for a few minutes, then feel the first stage)
This adiabatic cooling can cause ice to form in colder water. Since piston regs are usually not environmentally sealed (I have never seen one, may be wrong here), you can have ice form inside the regulator around the HP seat, which will prevent the piston from sealing properly. Since the HP seat doesn't seat, this causes an increase in the Intermediate pressure, and will force the valve open on the second stage.
Note that this is the failure mode that you want, since it still supplies air.
Diaphragm first stages avoid this with an environmental seal which keeps the environment water from entering the first stage, and causing freeze ups.
My exposure to piston regs is somewhat limited. I have always dove and worked on diaphragm regs. They have more parts, but are more reliable in colder water.
CrazyDave
Contributor
I was just glad that we did all the right things. That was my first experiance using those skills that we had been taught in real life.
Any time you or Steve want to go out just holler. I will have you as a Buddy any day.
Any time you or Steve want to go out just holler. I will have you as a Buddy any day.
Basically, what happens with a first-stage freeze is this:
1. The gas expands (the entire point of the reg is to drop the 3,000 psi of the tank, or whatever it is, to the IP for the second stage) and as the gas expands it cools (the exact opposite of what happens when you fill a tank and it gets hot. Heat is, in the gross physical sense [simplified!] the representation of the "vibration" of the molecules in a substance; at absolute zero there is none. If you double the volume of a gas, you half its pressure, and the same amount of "vibration" in the molecules now takes place in twice the space - hence, the temperature falls.)
2. The cold gas absorbs heat energy (cold is the absense of heat) from the regulator parts in an attempt to come to an equilibrium. The parts closest to the orifice (the HP seat) where the expansion takes place give up the most heat, since the gas temperature rises as it absorbs heat while it travels towards the reg. In a piston regulator, this is the piston "knife edge" where the seat is, and the bore of the piston as the gas travels down it.
(BTW, this is why, beyond tank corrosion issues, having very DRY air is important - if its NOT dry then the moisture in the AIR in the TANK can freeze in the reg - irrespective of whether you are using a piston or diaphram design! Bad news!)
3. The problem occurs because a short distance down the piston bore there is an O-ring and, on the other side of that O-ring, the water that you are diving in. This water gives up some of its heat to the piston and, in doing so, can freeze.
4. The coldest part of the piston in contact with the water is right at the high-pressure O-ring. Unfortunately, in order for the reg to work, the piston must slide through this O-ring to seal and unseal as the gas is breathed. If ice jams in the space between the piston and the O-ring, it cannot move and will not be able to seal.
5. The result of this is that the 1st stage will continue to supply gas even though the intermediate pressure has been reached. This does two bad things - it will overcome the spring pressure in your second stage, thereby causing a freeflow, AND, since gas continues to flow, the piston gets COLDER STILL! That causes yet MORE heat to be drawn from the surrounding water, and even MORE ice to form.
Once this gets started it gets worse FAST, because you are supplying yet more heat-robbing expansion of supply gas that is lost to the freeflow. The only solution is to shut down that regulator and allow it warm up. By definition if you are diving the water must be above the freezing point - otherwise it would be a block of ice and you couldn't swim in it! Unfortunately, on a single's rig used for recreational diving, you don't happen to have a second 1st stage handy to use while the first one warms up!
Ok, so what can we do about it?
Essentially, we must keep the water away from critical parts of the reg, so that if it freezes, it does not prevent the parts that move inside from doing so. If we can do that, the reg does not "freeze up" and there is no problem, even if the exterior was to become a huge icicle.
We can do this one of three ways:
1. We can encase the entire reg in air, and "seal" it, then arrange for some other material (say, an external diaphram) to transmit outside pressure to the inside, so that the balancing function (which is the point of water being allowed in the reg in the first place - to balance increased pressure as depth increases) can be done without water getting inside. This is how a diaphram reg does this job. They seal the water outside, and while it can freeze, it won't hurt anything if it does. It presses on a diaphram on the outside of the reg, which transmits that pressure to the actual regulating diaphram inside through the means of a rod or lever. At no time does water get where it can jam the mechanism if it freezes.
2. We can fill the parts of the reg near the piston with something that is (1) very viscous, so it doesn't leak out and make a mess, (2) is not compressible, as is true of most liquids and semi-solids, and (3) will not freeze. This is done with some piston regs. The cavity where water would usually go is filled with either silicone or christolube, and then a trim ring is placed over the balance chamber holes with a very small hole in it to allow water to press upon the grease. Since the silicone grease (or Christolube) will not freeze, the problem is solved. However, this is messy as all get-out when it comes time to service the reg, since you have to clean all the old grease out of there, and it CAN be messy in between if some of the grease leaks! It also has a potential secondary problem, in that the grease can trap some water in the reg when you're done using it, and that water (especially if its SALT water) can cause severe corrosion damage over time, since it cannot be rinsed out and won't dry out.
3. We can try to EITHER (1) keep water away from the parts of the reg that can bind up and freeze, and thermally insulate the cold parts of the piston such that not enough heat is transferred from the water to the cold piston to freeze the water, or (2) INCREASE the flow of water through the balance chamber so that it doesn't stay in contact with the cold piston long enough to give up sufficient heat to freeze. This is what SP and some others have attempted with their "thermal insulating" systems. The problem with this is that it is not foolproof, since you can reduce but never eliminate the transfer of heat, and in some ways insulating the piston actually makes the problem WORSE, in that the colder the piston the more heat it desires to transfer from the water. IF the integrity of these mechanisms to prevent water contact fails for any reason, you will get an instant flash-freeze, as opposed to a gradual problem building. So these systems are in some ways useful, and in other ways counterproductive (especially when they fail to work!) SP has been at this general game for a loooong time with varying degrees of success. That they keep changing it says everything you need to know about their ability to actually accomplish the goal - if they had found "the answer", they wouldn't have a reason to change it all the time, would they?
IMHO the best solution to cold water (under 50F) is a sealed diaphram regulator. Second-best is a piston reg filled with grease. Third is attempting to keep the water from freezing but letting it in there anyway.
For those who dive in warmer water, however, piston regs have certain advantages. They have far fewer parts in them than a diaphram reg, which means they are less likely to fail and are easier to fix when they do. They also generally have the ability to deliver more gas than a diaphram, all things being equal, because the gas passages inside are both larger and more direct. Finally, because the gas path and area involved in items like seats are larger, they are more tolerant of abuse, such as accidental ingestion of water into the gas pathways. This does not mean you don't have to be careful about getting water down the inlet (you do!) but that if some DOES get down there it is less likely to cause severe and immediate damage with a piston than it is with a diaphram regulator.
Any idea as to how much it costs to environmentally seal a piston reg?
This is a common problem with some ScubaPro regs. The piston simply freezes up in cold water. I witnessed the same thing happen to a diver with a ScubaPro reg set last week at 80 feet, and in only 45 degree water. A ScubaPro service tech was onsite that said that this is a common problem with some ScubaPro regs.
Noone else who was diving that weekend in the same conditions out of about 40 plus divers had any problems with their regs in the cold water. Most everyone had piston regs. The dive operator said he's seen this same thing 4 or 5 different times, and said that it has been ScubaPro regs everytime it's happened. Sounds like ScubaPro needs to do some recalls.
I suggest that you call ScubaPro, and voice you problem, and concerns asap! Don't screw around with bad equipment. Make them make it right, or get it replaced with a different type reg. that doesn't have this flaw.
Splash
Noone else who was diving that weekend in the same conditions out of about 40 plus divers had any problems with their regs in the cold water. Most everyone had piston regs. The dive operator said he's seen this same thing 4 or 5 different times, and said that it has been ScubaPro regs everytime it's happened. Sounds like ScubaPro needs to do some recalls.
I suggest that you call ScubaPro, and voice you problem, and concerns asap! Don't screw around with bad equipment. Make them make it right, or get it replaced with a different type reg. that doesn't have this flaw.
Splash
Ths Scubapro Mk 10 used a Silicone Protected Environmental Chamber (SPEC) which was Scubapro marketing speak for a silicone filled ambient pressure chamber. The early Mk 10's had small holes in the ambient pressure chamber and used no trim ring. This could get messy if you left your reg in the trunk of your car in July. The later Mk 10's as well as the Mk 15's used a rubber ring to cover the holes and contain the silicone. This was less messy when things got hot.
Both were very effective in preventing freeze ups. The only caution being the need to top off the silicone after 20-30 dives to replace the small amount that inevitably leaked out. This is was easy to do with the tubes of silicone availble or with a small syringe.
SP introduced parts of what became the TIS kit on the Mk 15 but also used the SPEC system. Eventually however SP recomended they not be silicone filled, but I fill 'em anyway because the SPEC system is way more effective than the TIS system.
The Mk 20/25 is less likely to freeze if you minimize the flow rate by 1) not being an air hog, and 2) not inflating a BC or dry suit and breathing at the same time. Using a LP steel tank at 2250 to 2640 psi also helps as the pressure drop and the amount of heat that the air has to absorb as the pressure decreases is reduced.
Genesis desribes the freeze process pretty well. But the piston is cooled along it's entire lenght including the head of the piston and the most likely area for a freeze up is near the head of the piston. Given the areas involved there is simply much more heat absorbed at the head of the piston than near the seat or around the shaft near the HP o-ring.
The head of the piston is chilled as is the entire intermediate pressure chamber as the whole area is exposed to the expanding air. SP changed to a piston with a composite head to reduce it's ability to transmit heat, but the first stage body around the ambient chamber case is still cooled via the metal surrounding the IP chamber. The "normal" freeze up is consequently not around the piston shaft near the HP seat but rather on the wall of the ambient pressure chamber just below the piston head. The piston head moves up when the reg flows air and if ice forms beneath it, the piston is unable to travel back down to contact the seat and stop the flow of air.
The Mk 20 and Mk 25 sported progressively larger holes in the ambient pressure chamber as a means of flowing more water through it and on the MK 25 AF, SP has added fins to improve heat exchange in this area to try to reduce the problem.
The piston shaft itself is mirror finished and even if ice forms in the very small clearance between the piston and first stage body, it is unlikely to prevent the piston from moving.
The TIS kit is designed to insulate the head of the piston and the shaft near the head of the piston that would otherwise be exposed to the water. Plastic shims are also used to isolate the spring from direct contact with other metal surfaces to reduce the transfer of heat from the spring to the rest of the reg.
The problem with the Mk 20 and 25 is that they are capable of flowing huge amounts of air with consequent demands for huge amounts of heat required by the expanding air. SP really needs to consider going back to a SPEC system on the MK 25 and be less concerned about how much of a mess they are to service.
I am pretty dubious that SP can ever design the reg to draw enough heat from the surrounding water or adequately insulate the critical areas short of lining the entire IP pressure area with an insulating plastic, and this could create major problems in terms of durability and Nitrox compatibility. Silicone grease was cheap, simple and effective, and they should have stuck with it.
Having said that I dive a Mk 20 and a Mk 25 on at least 100 dives per year all of them in cold water (35 to 45 degree bottom temps) and have never had a freeze up with either of them. But then I have low air consumption and dive 2475 psi tanks.
Both were very effective in preventing freeze ups. The only caution being the need to top off the silicone after 20-30 dives to replace the small amount that inevitably leaked out. This is was easy to do with the tubes of silicone availble or with a small syringe.
SP introduced parts of what became the TIS kit on the Mk 15 but also used the SPEC system. Eventually however SP recomended they not be silicone filled, but I fill 'em anyway because the SPEC system is way more effective than the TIS system.
The Mk 20/25 is less likely to freeze if you minimize the flow rate by 1) not being an air hog, and 2) not inflating a BC or dry suit and breathing at the same time. Using a LP steel tank at 2250 to 2640 psi also helps as the pressure drop and the amount of heat that the air has to absorb as the pressure decreases is reduced.
Genesis desribes the freeze process pretty well. But the piston is cooled along it's entire lenght including the head of the piston and the most likely area for a freeze up is near the head of the piston. Given the areas involved there is simply much more heat absorbed at the head of the piston than near the seat or around the shaft near the HP o-ring.
The head of the piston is chilled as is the entire intermediate pressure chamber as the whole area is exposed to the expanding air. SP changed to a piston with a composite head to reduce it's ability to transmit heat, but the first stage body around the ambient chamber case is still cooled via the metal surrounding the IP chamber. The "normal" freeze up is consequently not around the piston shaft near the HP seat but rather on the wall of the ambient pressure chamber just below the piston head. The piston head moves up when the reg flows air and if ice forms beneath it, the piston is unable to travel back down to contact the seat and stop the flow of air.
The Mk 20 and Mk 25 sported progressively larger holes in the ambient pressure chamber as a means of flowing more water through it and on the MK 25 AF, SP has added fins to improve heat exchange in this area to try to reduce the problem.
The piston shaft itself is mirror finished and even if ice forms in the very small clearance between the piston and first stage body, it is unlikely to prevent the piston from moving.
The TIS kit is designed to insulate the head of the piston and the shaft near the head of the piston that would otherwise be exposed to the water. Plastic shims are also used to isolate the spring from direct contact with other metal surfaces to reduce the transfer of heat from the spring to the rest of the reg.
The problem with the Mk 20 and 25 is that they are capable of flowing huge amounts of air with consequent demands for huge amounts of heat required by the expanding air. SP really needs to consider going back to a SPEC system on the MK 25 and be less concerned about how much of a mess they are to service.
I am pretty dubious that SP can ever design the reg to draw enough heat from the surrounding water or adequately insulate the critical areas short of lining the entire IP pressure area with an insulating plastic, and this could create major problems in terms of durability and Nitrox compatibility. Silicone grease was cheap, simple and effective, and they should have stuck with it.
Having said that I dive a Mk 20 and a Mk 25 on at least 100 dives per year all of them in cold water (35 to 45 degree bottom temps) and have never had a freeze up with either of them. But then I have low air consumption and dive 2475 psi tanks.
I don't have the expert knowledge that others on this board have, but I have learned a tip on how to avoid freeflows from our local ice divers.
The local practice is not to breathe from the second stage until you begin the descent(ie:underwater), and do not allow the second stage to get wet before that time. Can be a strange site, seeing a bunch of divers wading out and holding thier regs up, but it does seem to work. Freeflows are rare for our ice divers, but when one does occur, having the reg checked at the LDS is a must-do! If it happened once, it can, and may happen again. Find out why!
I use a Sherwood Maximus(piston 1st stage) as do many fellow divers up here. Several are ice divers and have not had problems with freeflows. After reading the previous posts about piston-type regs and freeflows, I was surprised that there weren't more problems in my area. Water temp at depth in Lake Champlain is 40+, even during the summer. I'm not trying to sell this reg, just giving everyone some backround to go on. Maybe piston-type regs can be more reliable just by the way we use them.
Jetwrench
The local practice is not to breathe from the second stage until you begin the descent(ie:underwater), and do not allow the second stage to get wet before that time. Can be a strange site, seeing a bunch of divers wading out and holding thier regs up, but it does seem to work. Freeflows are rare for our ice divers, but when one does occur, having the reg checked at the LDS is a must-do! If it happened once, it can, and may happen again. Find out why!
I use a Sherwood Maximus(piston 1st stage) as do many fellow divers up here. Several are ice divers and have not had problems with freeflows. After reading the previous posts about piston-type regs and freeflows, I was surprised that there weren't more problems in my area. Water temp at depth in Lake Champlain is 40+, even during the summer. I'm not trying to sell this reg, just giving everyone some backround to go on. Maybe piston-type regs can be more reliable just by the way we use them.
Jetwrench
may be a "dry bleed" reg.
Sherwood makes a number of dry bleed firsts, which have an interesting way of taking care of this problem. They slowly (intentionally!) bleed air into the balance chamber, and release any extra to the water. As a result they have the balance function without needing to get water in there!
Its a unique and VERY EFFECTIVE system that prevents freezes, as no water is in there! They also bubble from the first normally, which your buddy may think means you have a leak (until you explain it to him anyway)
This design's only problem is that if you "bomb" a dive (that is, decend very quickly) you can overrun its ability to keep up with the balance function, and as a result it can be hard to breathe until it catches up.....
Sherwood makes a number of dry bleed firsts, which have an interesting way of taking care of this problem. They slowly (intentionally!) bleed air into the balance chamber, and release any extra to the water. As a result they have the balance function without needing to get water in there!
Its a unique and VERY EFFECTIVE system that prevents freezes, as no water is in there! They also bubble from the first normally, which your buddy may think means you have a leak (until you explain it to him anyway
)This design's only problem is that if you "bomb" a dive (that is, decend very quickly) you can overrun its ability to keep up with the balance function, and as a result it can be hard to breathe until it catches up.....
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