What is Intermediate Pressure?
Your basic diving equipment consists of a Cylinder and Regulator and in that combination you have three sets of pressure:
1. The Cylinder Pressure
2. The First Stage Pressure; and
3. The Second Stage Pressure
1. The Cylinder Pressure
2. The First Stage Pressure; and
3. The Second Stage Pressure
From your open water theory and your Equipment Speciality you know that the first stage takes the pressure from the cylinder and 'converts' it into low pressure - the pressure that you can breath
How to Measure Intermediate Pressure
What you need is a cylinder with 206 bar (3000 PSI) or more air in it and a regulator set and an Intermediate Pressure Gauge.
There are two type of Intermediate Pressure (IP) Gauges - one is a gauge that has a safety relief valve and one that does not
There are two type of Intermediate Pressure (IP) Gauges - one is a gauge that has a safety relief valve and one that does not
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The gauge ideally will have a scale of 0-20 or 0-25 bar (0 – 300 or 0 – 350 bar).
NB. If your pressure gauge is not fitted with a safety relief valve (bleed valve), make sure a (downstream) second stage is connected.
To take a measurement connect your pressure gauge to a low pressure port of the first stage (BCD or Drysuit hose). Slowly turn on the cylinder, the needle for depending on model and brand should stop in the 8.5 to 10.3 bar range and remain stationary (Apeks regulators 9 - 10 bar).
If the pressure gauge rapidly exceeds 10 bar (145 PSI) there is a High Pressure (HP) leak. Quickly close the cylinder valve and purge the second stage or open the bleed valve and close the cylinder valve. Failure to do so may cause a rupture to the MP hose and / or MP Gauge, potentially leading to personal injury.
The point where the needle stops and remains stationary is called the lock-up pressure. After your initial reading, give the second stage a gentle purge – or a couple of gentle purges - and evaluate the reading (lock-up pressure) once more. During the purge, the intermediate pressure is expected to drop then to rise again once the purge is over. It should not drop below the recommended lower range i.e. 9 Bar in the case of most Apeks regulators.
Now that you have established the value of the intermediate pressure, you have to compare the reading with the recommended value by the manufacturer and decide if this reading is acceptable or not.
It is important to pay attention to the fact that the specifications given by the manufacturer are related to a set supply pressure and this supply pressure is most often high supple pressure or a high supply pressure range. So check the literature as not to get caught out. Hence it is important to make sure that your supply pressure is within that specified range in order to make any proper observations.
NB. If your pressure gauge is not fitted with a safety relief valve (bleed valve), make sure a (downstream) second stage is connected.
To take a measurement connect your pressure gauge to a low pressure port of the first stage (BCD or Drysuit hose). Slowly turn on the cylinder, the needle for depending on model and brand should stop in the 8.5 to 10.3 bar range and remain stationary (Apeks regulators 9 - 10 bar).
If the pressure gauge rapidly exceeds 10 bar (145 PSI) there is a High Pressure (HP) leak. Quickly close the cylinder valve and purge the second stage or open the bleed valve and close the cylinder valve. Failure to do so may cause a rupture to the MP hose and / or MP Gauge, potentially leading to personal injury.
The point where the needle stops and remains stationary is called the lock-up pressure. After your initial reading, give the second stage a gentle purge – or a couple of gentle purges - and evaluate the reading (lock-up pressure) once more. During the purge, the intermediate pressure is expected to drop then to rise again once the purge is over. It should not drop below the recommended lower range i.e. 9 Bar in the case of most Apeks regulators.
Now that you have established the value of the intermediate pressure, you have to compare the reading with the recommended value by the manufacturer and decide if this reading is acceptable or not.
It is important to pay attention to the fact that the specifications given by the manufacturer are related to a set supply pressure and this supply pressure is most often high supple pressure or a high supply pressure range. So check the literature as not to get caught out. Hence it is important to make sure that your supply pressure is within that specified range in order to make any proper observations.
Why should A Diver measure their Intermediate Pressure
Monitoring your intermediate pressure is one way of monitoring the health and status of your regulators. In general, an IP that is not in the correct range and steady can indicate 1) a harder work of breathing (WOB) than normal, or 2) a tendency toward 2nd stage free-flow.
Slowly increasing IP (creep) usually indicates a bad high pressure seat which can cause something as simple as a temporary free-flow, or as dangerous as a catastrophic failure in the first stage, second stage, or hose. The failure mode depends on the kind of regulator.
Slowly increasing IP (creep) usually indicates a bad high pressure seat which can cause something as simple as a temporary free-flow, or as dangerous as a catastrophic failure in the first stage, second stage, or hose. The failure mode depends on the kind of regulator.
Version 1:00 March 2021