U-tube manometer

[burna]

I am getting myself ready to strip down my old [spare] regs and learn to service them.

They are Oceanic SP5/Alpha 8, they haven't seen a lot of work over the last 18-24 months and still breathe fine, could prob'ly do with a check out and clean though.

I have just made my own manometer based on herman's design. (Thanks herman.)

Checking my old primary (which is now going on my bailout bottle) the cracking pressure still comes up with a respectable 1.125" which is within the specs of 1.1-1.5".

One thing I have found is it is very hard not to get the gauge 'bouncing', you really have to draw on the reg very smoothly so as to get an accurate result. I am wondering whether there is a way of dampening this, maybe by putting in a small restriction at the bottom of the 'U' to slow the water movement.

Obviously this would slightly reduce the responsiveness of the gauge tho'.

Next is to order an I.P gauge I think should help detect exactly when the reg 'cracks'.

Would be interested in some feedback.

 

[a878bob]

mine setup is very similiar. But the 2nd stage side tubing is much shorter. cut it down some and see if that helps.

 

[fppf]

If you only use the large tubing in the gauge section and then reduce it to 1/8" tubing to the reg that will help a lot. Gas is compliant, it will act as a spring. Also, if you put a section of hard PVC to the reg you can drill a small hole at an angle toward the reg and shove the tubing through it. Having the tubing 90 degrees from the flow of the gas can actually generate a small error. When your testing what you will notice with many regs is as you very slowly draw a vacuum on them the pressure will decrease until they crack. Once they crack and start to flow a little you will see the pressure increase again. IE it may crack at 1.5" but then drop to 1" while its flowing. You can hook a vacuum cleaner up with a PVC gate valve (grainger for about $17) and then get really accurate smooth readings.

Throw some food coloring in the water and its easier to read.

IP gauge really wont show the second stage cracking. But make sure you get a good quality gauge, not something used on a welding cylinder. I buy pressure transducers off ebay and then industrial panel meters for really nice accurate digital readouts. You can get both pieces for maybe $50 if you play your cards right. That's cheaper then some of the super cheap crap gauges.

 

[dannobee]

Reduce the size of the tubing. Also, any kind of restriction will help dampen out the pulses. An old carburetor jet would probably suffice; just stick in inline somewhere.

It looks like you're reading it correctly to get 1-1/8" H20, but just to be sure, you either double the change on one side, or add the difference between the side dropping and the side rising.

Most manometers (the professional ones, for whatever that's worth) have a scale between the tubes and you add up the difference between the high and low sides. The scale has a slot and is held in place with a thumbscrew so that instead of trying to add a few drops of water to zero it out, you just move the scale a bit.

 

[fppf]

Or, the easiest way....
MAGNEHELIC PRESSURE GAUGE DWYER #2008 - eBay (item 180488803837 end time Apr-08-10 09:14:05 PDT)

I think I paid $10 for mine with shipping

 

[herman]

........................Throw some food coloring in the water and its easier to read.

I like blue in mine. I also keep a syringe with water in it by the manometer to add small controlled amounts of water when needed.

IP gauge really wont show the second stage cracking. But make sure you get a good quality gauge, not something used on a welding cylinder. .......................


A slight dip in the IP indicates when flow has started and when used in conjunction with a manometer or magnehelic the exact cracking pressure is easier to measure.

Or, the easiest way....
MAGNEHELIC PRESSURE GAUGE DWYER #2008 - eBay (item 180488803837 end time Apr-08-10 09:14:05 PDT)

I think I paid $10 for mine with shipping

Now you need a manometer to check it's calibration.

 

[Bubbletrubble]

I guess having a manometer or magnelic might be nice if you wanted to quantify the cracking pressure. But is it really necessary? I've always used subjective inhalation for tuning purposes. Find the tipping point for freeflow and then turn the orifice back a smidge. If it's too difficult to exhale, I'll change the exhaust valve. Am I missing something here?

 

[fppf]

Now you need a manometer to check it's calibration.

Or just have a friend that works in the calibration industry
I have found the magnehelic's to be very stable. I have not needed to adjust mine at all. But they are mounting sensitive and may need a zero adjust if you change there orientation. IE gravitiy effects them. If it does need cal its best to send them to the factory, there a PITA to adjust the span settings.

But the same is true for your manometer, it needs to be level and perpendicular to the force of gravity. So in a sense it needs cal too.

 

[fppf]

I guess having a manometer or magnelic might be nice if you wanted to quantify the cracking pressure. But is it really necessary? I've always used subjective inhalation for tuning purposes. Find the tipping point for freeflow and then turn the orifice back a smidge. If it's too difficult to exhale, I'll change the exhaust valve. Am I missing something here?

While you can feel if a reg is tuned good very easily, a mag or manometer can clue in to over adjustment issues. If you tighten the orifice to much it can limit the amount of stroke on the poppet. This will limit the max flow rate, which at depth can be bad.

Testing a reg at higher flow rates with a mag can detect this condition. You will see an increase in breathing resistance as the poppet bottoms out.

 

[herman]

I guess having a manometer or magnelic might be nice if you wanted to quantify the cracking pressure. But is it really necessary? I've always used subjective inhalation for tuning purposes. Find the tipping point for freeflow and then turn the orifice back a smidge. If it's too difficult to exhale, I'll change the exhaust valve. Am I missing something here?

For most work, not really, it's your reg and if you are happy then all is good. With a little practice you can achieve a "calibrated" inhale and exhale...still you need some way of measuring the result until you get good at judging what 1 in of water feels like. I am often playing with different setting and mods on regs so I really need something that can show me slight changes in cracking and/or exhaust pressure. Considering the simplicity and low cost of a manometer there is really no reason not to make one. Even magnehelics on ebay can be had for fairly low cost so why not have one or the other....or both.