Well Regulated

Well, we received a request for another techie blog, so we turn to out resident equipment guy, Mike!

Customers and divers often ask me to how a regulator works and why it’s called a Regulator. The second part of the question is easy. It’s called a regulator because the first stage regulates the pressure from the tank to the 2nd stage. It takes the pressure from a full tank at 3000 PSI to 135-140 PSI in the low pressure hose between the 1st and 2nd stage. This is called the intermediate pressure. Because your respiratory system can only tolerate a differential of about .14 atm/bar you wouldn’t be able to breathe though a hose at 10 ft.   The increased atm/bar would be enough to not allow you to draw in a breath of air. The regulator delivers air at a pressure the same as the pressure of the water surrounding you and continues to increase or decrease the pressure as the exterior water pressure changes around your body. The regulators that we use today are called open circuit regulators.

Scuba regulators are also called demand regulators because they deliver air on demand when you inhale. First stages generally are either a piston or diaphragm design. They both use external ambient water pressure and a spring to open the valve inside the first stage when the pressure on the low pressure side of the 1st stage drops below 135-140 PSI.  In the piston regulator the external water pressure and primarily the spring forces the valve open when the pressure drops on the low pressure side of the regulator. As pressure comes back to the intermediate pressure the piston moves back and closes the valve. The spring does most of the work but if the spring chamber was not open to the water coming and going the chamber would create a vacuum and the valve would not be able to open or close. To set the intermediate pressure on a piston regulator the unit must be disassembled and shims added or removed to get the right spring setting.  

A diaphragm regulator works on the principle of an open circuit system with one major difference. In a piston model, the valve set remains fixed and the valve orifice on the end of the piston moves opening and closing the valve.  On a diaphragm regulator, when the intermediate pressure drops on the low pressure side, the spring pushes on the diaphragm that pushes on a pin that opens the valve by pushing the valve seat away from the valve orifice, opening the valve. As the intermediate pressure returns to the intermediate chamber it pushes the diaphragm in the opposite direction and it closes the valve maintaining 135-140 PSI in the low pressure supply line.

The second stage is the final piece to the SCUBA system. There are a variety of internal designs in the second stage ranging from a simple rocker arm and single spring to a more complicated shuttle valve and multiple spring designs. They all deliver breathing air but the shuttle valve second stages are much easier breathing. (Manta divers only sells the better balanced first stage and shuttle valve second stages regulators. The Atomic Z2, Aqua Lung Legend LX Supreme and Titan LX Supreme are the only regulators that you will find in our rental Fleet). The diagram attached is a rocker arm and spring design. So here’s how they work. The air in the second stage is always equal to the ambient pressure on the outside of the regulator whether you’re at the surface or at depth.  If you closed up the mouth piece on a pressurized second stage and lowered it down to 100Ft depth, all the way down the ambient pressure would push on the diaphragm and the rocker arm would open the valve until the PSI in the second stage equaled the ambient pressure outside of the second stage. When they are equal the valve closes and the pressure is equalized. If you slowly brought the pressurized second stage back to the surface the ambient pressure would become less than the PSI in the second stage and the pressure would equalize by venting though the exhaust valve.

That being said here’s how the open circuit SCUBA regulator system works. (It’s called open circuit because the air is exhausted and not returned to the supply).  As you start your dive with each breath you take it reduces the PSI inside the regulator causing the ambient pressure to push in the on the second stage diaphragm and pushes on the rocker arm opening the valve in the second stage. It only opens the valve enough to deliver ambient pressure and closes the valve when the pressure is equal.  The air delivered to the second stage reduces the intermediate pressure in the low pressure hose and the low pressure chamber in the first stage. When the pressure in the first stage chamber drops below 135-140 PSI the first stage spring pushes on either the piston or the diaphragm opening the first stage valve. When the intermediate pressure returns to 135-140 PSI it pushes back on the spring and closes the valve.  Every time you take a breath the cycle is repeated.

Because your life depends upon your regulator it pays to keep your regulator in top shape. Most manufacturers recommend inspection every other year and rebuild on the off years.  Although you could make your own rebuild kits it highly recommended that you only use the manufacturer’s kits.

By the way, we are looking for guest bloggers to share their diving stories.  Where have been diving lately?  Tell us stories about your training.  Share some trip photos and a report about a dive destination.  The information in the blog must be your own words, and accompanied by a photo or two. Please send it in Word document form to mantadiveshop{at} a yahoo account. (Security against bots. Sorry!)  Just to sweeten the pot, if we post your blog, you will receive a FREE Manta Divers T-shirt!

As always, like us on Facebook, share the blog and/or leave a comment for some feedback. If you have a question for Mike, let us know in a comment! Until next time, cheers!