How to Choose the Right Sidemount Cylinders

There seems to be a tendency for newer sidemount divers to think all, or at least most, cylinders are created equal. This isn’t the case. Cylinders, whether sidemounted or backmounted, will have some very similar results when it comes to different volumes. However, when it comes to buoyancy characteristics, cylinders will vary. Choosing the right cylinders is one of the most important decisions you will make when configuring your sidemount diving system.

Pair Matching
What Size Cylinders Should You Get?
How Do Cylinders Differ From Each Other?
Common Mistakes Made

Pair Matching

Let’s look choosing your set of sidemount cylinders. Just as in backmounted, manifolded doubles, you must pair match your cylinders. It not a matter of making sure they are the same length – a 1/4 inch difference in length won’t affect your setup. It’s the buoyancy characteristics of the cylinders that affect alignment and trim. I had a student that bought a pair of cylinders but ended up buying one cylinder from one location and the other from a different location. With a quick glance, the cylinders appeared identical. The differences did not become evident until during the first dive.

When we got in the water, the first thing I noticed was that this student was listing to one side. I knew the rigging was identical on both sides because we had just set it up. (The Sidemount Diving Guide explains in detail why it’s so important to ensure that your rig is symmetrical.) After we got out of the water, we examined his sidemount rig and the shoulder straps were evenly spaced on the waist strap. Nothing was off kilter. He shouldn’t have been off kilter either.

I looked at his cylinders. One had a much more defined transition from the body of the cylinder to the neck while the other was a much more gradual transition. I checked the manufacture dates. They were different. We placed the cylinders in the water with both having very similar pressures, and they even rested differently in the water. Their buoyancy characteristics were dissimilar enough that they caused a significant difference in trim in the water.

What Size Cylinders Should You Get?

Let’s look at the next mistake often made by newer divers – bigger cylinders mean more bottom time. This isn’t necessarily true. Often times, bigger cylinders simply mean more drag in the water, which in turn means more effort to move through the water. More effort equates to higher gas consumption. Bigger cylinders could mean less bottom time due to this.

When I first went back to backmount after a year of strictly diving sidemount I grabbed a set of LP108s. A couple days later I decided to try a different set of cylinders, a set of LP85s. I reached my turn pressure in each set of cylinders at the same location in the cave. I used almost 20 cubic feet less on the same dive using the 85s than I did using the 108s. The additional drag and subsequent effort of moving the larger and heavier cylinders resulted in a much higher gas consumption.

How Do Cylinders Differ From Each Other?

The cylinders I prefer for a majority of my diving are LP85s and LP95s. They are all on the smaller side but provide sufficient gas to do decent length dives. However, even these cylinders are not created equally. Cylinders have different buoyancy characteristics dependent on the manufacturer. This is the case whether they are the smaller cylinders listed here or the larger cylinders such as LP108s and LP 120s.

What this means is that two sets of LP85 may not trim out the same if the rigging is identical because of their buoyancy characteristics.

Common Mistakes Made

  • Not buying pair matched cylinders
  • Buying large volume cylinders for basic diving
  • Treating all cylinders as equal

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Related Articles

How to Properly Manage Gas in Your Cylinders
How to Choose Proper Hose Lengths
Proper Sidemount Cylinder Rigging: What Matters Most
Proper Sidemount Stage Rigging for Cave Diving
How to Properly Rig Top Mounted Stage Cylinders
Common Modifications of the Dive Rite Nomad

For a complete overview of how these elements work together, see The Complete Guide to Sidemount Diving Configuration.