Regulator Testing Equipment

[herman]

Herman, by "test" do you simply mean breathe thru the second stage...ie no tools or gauge, make sure no free flow?
I have done this and find the adjustment zone is +/- 1/4 turn and I set to middle.

Can you relate how much the IP typically varies from 3000psi down to 300psi? Presume that nominal is 140psi going to second stage.
Next obvious qs is why do you need a full tank to set the second stage if the first stage keeps the IP below 160psi, and the mechanism is such that the balanced effect is such that the air draw would be most problematic at the lowest IP you could see, not the highest? I would think that 300psi tank pressure would be most important in setting the 2nd.

All comments appreciated,
Stew

"Test" can mean pretty much what you want it to. A simple “no freeflow/feels good to me” is acceptable to some people. I like to have some quantitative measure the base my go/no go decision on. A simple dunk the second stage in water and see where it cracks open works well but the best inexpensive way is to build yourself a U tube manometer. They can be made for less than $5, are accurate and easy to use.
I now have several magnehylics but still keep a manometer on the bench and use it from time to time.

Set up of the second stage (unbalanced second stages) is very dependent on the IP it is supplied with and IP shift, if any, needs to be accounted for. As IP shifts, the cracking effort of the second stage gets higher as the IP drops. Conversely, cracking pressure decreases as IP rises until the point where the second stage opens and bleeds off pressure. For balanced first stages, tank pressure as long as its above 300 is not is much of an issue since the whole purpose of balancing a first stage is to keep IP constant across the range in tank pressure and in turn keep second stage cracking pressure constant. Most balanced first stages do a good job and keep the IP constant within 3-6psi or so, plenty close enough for home use. The problem comes when you start setting up unbalanced first stages with unbalanced seconds. With an unbalanced first stage, as tank pressure changes there is a corresponding shift in IP, for piston regs, the IP goes down as tank pressure goes down. I have seen 20 psi or greater shift from 3000 to 300 tank pressure in an unbalanced first stage. If you set up an unbalanced first and second stage with a tank pressure less than a full tank (the pressure could be 3500 or more if you use HP tanks) there is a good chance you will experience a freeflow when you connect the reg to a full tank. Higher tank pressure= higher IP= likely freeflow If you set the second stage with a 300 psi tank it will no doubt freeflow. The IP of unbalanced diaphragm regs increase as tank pressure drops and with those you must use a 300 psi tank to set up the second stage, otherwise it will also free flow when you attach it to a full tank. Lower tank pressure= higher IP= more likely freeflow It is unlikely you will ever see an unbalanced diaphragm reg unless you start working with vintage regs, it has been many years since an unbalanced diaphragm first stage has been sold.

 

[scorman]

Set up of the second stage (unbalanced second stages) is very dependent on the IP it is supplied with and IP shift, if any, needs to be accounted for. As IP shifts, the cracking effort of the second stage gets higher as the IP drops. Conversely, cracking pressure decreases as IP rises until the point where the second stage opens and bleeds off pressure.

Thanks Herman for your detailed explanation.
What I glean from above, is that if low test pressure is used (don't have access to full tank), then when a full tank is applied, there is a possibility of free flow. However, there is no danger of a setting whereby cracking pressure would prevent one from breathing normally at depth.
This was my major concern because free flow can easily be identified in wash tank at dive op before dive, but breathing could only be determined in situ where it is too late.

OT for general discussion here - is it better to have a slightly higher crack pressure w/r to better air consumption, or slightly lower to accommodate easier breathing. In short: is it better to have to suck slightly harder than to have air belched into your mouth??

Stew

 

[herman]

Thanks Herman for your detailed explanation.
What I glean from above, is that if low test pressure is used (don't have access to full tank), then when a full tank is applied, there is a possibility of free flow. However, there is no danger of a setting whereby cracking pressure would prevent one from breathing normally at depth.
This was my major concern because free flow can easily be identified in wash tank at dive op before dive, but breathing could only be determined in situ where it is too late.

OT for general discussion here - is it better to have a slightly higher crack pressure w/r to better air consumption, or slightly lower to accommodate easier breathing. In short: is it better to have to suck slightly harder than to have air belched into your mouth??

Stew

For unbalanced first stages yes, for balanced first, it should not matter (within reason) what the tank pressure is.
You would have to work hard to get a second stage to the point where you could not get any gas from it- by adjusting it, obviously you can if you damage/incorrectly assemble it. Even at high cracking pressures you can still get gas although it will not be much fun. The breathing resistance will not change underwater so if it's good at the bench, it will be good on a dive, again assuming it's assembled correctly.

Neither IMO, there is no need to have to work any harder than is necessary but a reg that is force feeding you air is not good either, if nothing else it waste gas. Setting a second stage to the manufactures specs is always a good way to go, esp for someone learning to set up a reg. Again it's a big help if you have some way of measuring the cracking pressure of your reg, build a manometer if for no other reason than to help you recognize what a good cracking pressure "feels" like. With some practice you can get a fair guess of how the reg is set up.

 

[halocline]

I think an AL80 or other 3000 PSI tank is slightly preferable to a LP72 for regulator testing, at least for the regs I usually work on. This is because you're often limited to 2250 PSI in a LP72, and as such, can't test the 1st stage at full tank pressure.

I have a 13cft pony that I use for two things, filling tires and testing regulators. I can easily refill it from another tank using two first stages with a HP hose connecting them. Couv was nice enough to put together a set of fittings to do that.

Awap's trick of bleeding down pressure by turning the tank valve off and bumping the purge to test the first stage at various pressures works perfectly, so if you have a full tank you can easily check the IP at any supply pressure. It is very interesting to see IP vary in supposedly 'balanced' first stages like the MK10 and MK11/17. In each of those cases a more-than 10PSI swing from full to empty is common. I've been able to minimize it the MK10 using duro 90 polyurethane o-rings for the HP piston, but it's still substantial. With the MK11 I was really surprised to see such a large IP rise as supply pressure drops; this is scubapro's balanced diaphragm 1st stage.

I use a torque wrench on the MK5 turret bolts, but since I've replaced most of my brass ones with the reproduction SS bolts, I don't think it's critical anymore. As mentioned, the reason for using a torque wrench in scuba regulators is to prevent over-torqueing. Supposedly there are studies that have shown most people will overtorque when guessing at a torque spec.

 

[WhiteSands]

Magnahelics are cheap and easy to find. But again there are alternatives. As part of the course I after we did the mag thing I showed him how to check it using a half a sink of water. Results were dang near the same. You can also make one with a board, clear tubing, a couple clamps or zip ties, and a ruler. The sink though works very well in the field. Or even a pan of water that the second will fit into comfortably.

Jim or anyone else,
care to elaborate on how the sink test is done?

 

[buddhasummer]

I've never done it that way but assuming my understanding is correct:

Put the second stage face down into a sink of water and measure at what point it cracks, should be before the mouth piece is covered with water. Around 1-1.5".

 

[herman]

Place the second stage into water with the mouthpiece facing up with no water in it. SLOWLY lower it until the reg just starts to open, then measure the distance from the water line to the face of the reg, that is the cracking pressure in "inches of water column" (or mm of water if metric). I would subtract about 1/4 inch from that number to get a closer aproximation since there is some space between face of the reg and the diaphragm which is where the measurement is actually supposed to be taken from. If the mouthpiece gets close to filling (or does) then the cracking pressure is too high, at least for a primary, octos will be a some deeper depending on tech preference and design. Reg specs differ but somewhere around 1 to 1.5 in is normal. If the reg has a venturi lever,set it to "-" or min. It will not affect the measurement but it will help prevent a freeflow and a face full of water. If the reg has a cracking pressure adjustment, it needs to be set to minimum or just tighter than a slight free flow. This a a good go/no go test that can be done anywhere in just a few seconds since it can be done to any reg in any water.

 

[divad]

This a a good go/no go test that can be done anywhere in just a few seconds since it can be done to any reg in any water.

There must be a wrench for that.

 

[scorman]

Place the second stage into water with the mouthpiece facing up with no water in it. SLOWLY lower it until the reg just starts to open, then measure the distance from the water line to the face of the reg, that is the cracking pressure in "inches of water column" (or mm of water if metric)...... If the mouthpiece gets close to filling (or does) then the cracking pressure is too high, at least for a primary, octos will be a some deeper depending on tech preference and design.

OK Herman, now you have almost totally confused me. Yes, I am taking your advice on building a manometer ..simple enough and I understand that entire concept. However, this dipping makes no sense to me. Cracking pressure is from a negative pressure created by breathing in, but dunking is a positive pressure exerted by the head of water. When you say "reg just starts to open", I read that to mean that it starts free flowing (bubbling)....

I must be missing something basic here ...please elaborate on your discussion unless your setup implies that the mouthpiece NEVER fills with water and the differential pressure is not "suction" but rather the differential of atmospheric pressure inside the dry mouthpiece and the slightly higher hydrostatic pressure of the water on the underside of the diaphragm.

thx,
Stew

 

[redacted]

I must be missing something basic here ...please elaborate on your discussion unless your setup implies that the mouthpiece NEVER fills with water and the differential pressure is not "suction" but rather the differential of atmospheric pressure inside the dry mouthpiece and the slightly higher hydrostatic pressure of the water on the underside of the diaphragm.

thx,
Stew

You got it. Does not matter whether you create the pressure differential with vacuum inside or pressure outside. A primary should start to flow well before the mouthpiece starts to take water on. I have a magnehelic but find the sink of water to be easier and faster.