SCUBA DIVING EQUIPMENT FIRST STAGE REGULATORS

SCUBA DIVING EQUIPMENT FIRST STAGE REGULATORS

Back again with some information regarding the first stage scuba diving regulator.

There are two basic first stage regulator designs the piston or diaphragm and then two versions of each design in the balanced or unbalanced.

With the Piston and Diaphragm first stage regulators the differences are:



In a diaphragm first stage, water pressure is transmitted to the valve through a flexible diaphragm. The valve itself is sealed against water intrusion, and the spring chamber can be easily sealed as well. Because water cannot enter the first-stage housing, internal corrosion is minimized. On the other hand, diaphragm first stages have more moving parts and may not lend themselves as well to swivel fittings for low-pressure hoses, because intermediate pressure comes out in the middle of the housing.




In a piston design, water pressure acts directly on the valve, making it simpler, with fewer moving parts. They are easy to adapt to swivel fittings, making low-pressure hose placement more convenient. But because water enters the spring and piston chamber, pistons are more sensitive to corrosion, especially if the owner neglects regular maintenance.



Balanced vs. Unbalanced

Both piston and diaphragm first stages come in balanced and unbalanced versions. A valve is balanced by extending the shaft beyond the pressure chamber so air pushes on both ends equally. A balanced first stage retains ease of breathing all the way down to the last few pounds of tank pressure, because intermediate pressure remains constant. These units are more complex and generally more expensive.

Until a few years ago, unbalanced first stages were severely affected by low tank pressures and would begin to breathe harder below about 700 psi. The reason was a 30- to 40-psi drop in intermediate pressure from full to near-empty tanks. But current models are less sensitive to supply pressure, with a pressure drop of only 20 to 30 psi. Therefore, the performance gap between balanced and unbalanced first stages has tightened. Unbalanced first stages are more economical, have fewer moving parts and are easier to service. But they will usually have fewer ports and lack the convenience of swivel mounting.

A simple description of the regulator first stage would be as follows;

The system operates like this:

1. You inhale, thereby lowering the pressure in the intermediate-pressure chamber to below the ambient water pressure.

2. The water pressure pushes inward, opening the valve or piston.

3. The open valve connects the high-pressure chamber with the intermediate pressure chamber.

4. Air flows from the high-pressure chamber into the intermediate-pressure chamber, thereby increasing the pressure in the intermediate-pressure chamber.


5. When the pressure in the intermediate-pressure chamber equals the ambient water pressure, the valve or piston closes.

6. The process repeats when you inhale again.

Look out for the next more detailed posts on Open Circuit SCUBA equipment Second Stages.

Please feel free to comment on any posts in this blog.


To find out more about SCUBA equipment available from Samui Dive Supply please contact us for more information.

SELF CONTAINED UNDERWATER BREATHING APPARATUS (SCUBA) (PART 2)

Self Contained Underwater Breathing Apparatus (SCUBA) (Part 2)

So if you have read the post SELF CONTAINED UNDERWATER BREATHING APPARATUS (SCUBA) (PART 1) I am sure you will now be aware that it is all a matter of bubbles. We will concentrate on Open Circuit SCUBA, the one which vents bubbles every time you breathe out, and its fundamental components.

There are four components to Open Circuit SCUBA equipment:

High Pressure Breathing Gas Cylinder

Your breathing gas cylinder will normally be manufacture of either Steel or Aluminum. It will have an outlet valve that opens or closes the cylinder and permits the second component of SCUBA, the regulator, to be attached to the cylinder. The working pressure of the cylinder can vary from 200 bar to 300 bar and vary in size from 8 litre cylinders, suitable for junior divers up to 15 litre cylinders, great for air hogs.

The Regulator

The SCUBA regulator is a two stage pressure regulator which provides you with your breathing gas on demand from you cylinder when you inhale. The first stage regulator will reduce the gas pressure from your cylinder to an intermediate pressure (IP), typically 9 – 10 bar, which in turn will then be reduced by the second stage demand regulator to the ambient pressure for breathing.

Your first stage regulator would also have fitted an alternative air source regulator (AAS) or octopus for sharing breathing gas with your dive buddy in an emergency situation, an gas pressure gauge (SPG) that indicates your current cylinder gas pressure and a low pressure inflator (LPI) hose which supplies gas to your BCD at the IP to assist with you buoyancy control.

Buoyancy Control Device (BCD)

The majority of recreational divers use an inflatable jacket style BCD to control their buoyancy. Through the use of the LPI connected to your cylinder via the LPI hose gas can be added to or released from your BCD to assist you in attaining either neutral buoyancy whilst under the water or make you positively buoyant for resting at the surface or surface swimming.

Your BCD will also include a backpack to which your cylinder will be attached using bands thus holding you SCUBA system together in one integral unit. When we cover the BCD in more detail in a later post we can discuss the different styles.

Weight Systems

When diving, you use a weight system to just offset any buoyancy. It may be on a weight belt around your waist, a harness on integrated into your BCD.



Look out for the next more detailed posts on Open Circuit SCUBA equipment.

Please feel free to comment on any posts in this blog.

To find out more about SCUBA equipment available from Samui Dive Supply please contact us for more information.

SELF CONTAINED UNDERWATER BREATHING APPARATUS (SCUBA) (PART 1)

Self Contained Underwater Breathing Apparatus (SCUBA) (Part 1)

A month or so ago, doesn’t time fly when you’re having fun, we said we will introduce SCUBA equipment to you, attempt to explain what it is and what it does for you.

As an introduction there are three basic types of SCUBA equipment:

Open Circuit

When you breath in you use a two stage regulator that provides gas at the ambient pressure from a tank of compressed gas usually at 200 bar. When you breath out through your regulator second stage the exhaled air vents into the water as bubbles. Your SCUBA equipment would also consist of a Buoyancy Control Device (BCD) and weight system. This is the system we will focus on in more detail in the next post. An example of an Open Circuit Regulator would be the Scubapro Mk25 1st Stage witha S600 2nd Stage.

Semi-Closed Rebreathers (SCRs)

When you breathe in, you breathe from a counter lung in your SCR. When you breathe out your exhaled air passes through a scrubber that removes the excess carbon dioxide in the exhaled air. This air then passes into the counter lung where it mixes with oxygen that is flowing at a continuous set flow rate to produce your breathing gas. Any excess gas in the counter lung is vented off as a small stream of bubbles. An example of a SCR would be the Drager Dolphin.

Closed Circuit Rebreathers (CCR’s)

When you breathe in, you breathe from a counter lung in your CCR. When you breathe out your exhaled air passes through a system that removes the waste carbon dioxide in the exhaled air and replaces consumed oxygen then it returns to the counter lung. There are no bubbles. An Example of a CCR would be the Pelagian from RebreatherLab.

Look out for the next post on Open Circuit SCUBA equipment.

Please feel free to comment on any posts in this blog.

To find out more about SCUBA equipment available from Samui Dive Supply please contact us for more information.