Hoses are often overlooked when buying and maintaining regulators and some have certain features that worry divers because they can look like a fault. Your hoses are an essential part of your setup and need due care and attention to keep them working properly. Caring for your hoses is pretty easy; don't leave them lying around in the sun, wash and dry them and store them as flat as possible. Most hoses have three layers; an internal rubber hose, a middle woven layer and an external protective coating.
At the core of every hose is a polymer hose that is used to transport and hold the gas inside. It will have a smooth internal lining for improved airflow but will be relatively weak and needs the other layers for strength. The internal core is probably the most important layer to look after and is unfortunately the one that you can't see. The core, like all rubber products, degrades with age and hardens until it cracks or splits. If water enters the hose at any time it must be flushed out carefully and dried out as pressurised water can damage your regulator.
BRAIDED MID LAYER
This is where the strength and flexibility of your hose comes from. The braided material holds the internal core from expanding but allows it to bend and flex as our hoses need to.
The outer coating protects the inner components from environmental damage. Usually made from a tough rubber the outer coating is a sacrificial layer that takes the bumps and scrapes but won't affect the function of the hose. You can often find tiny holes along the length of most hoses, these are a safety feature and are supposed to be there. The holes allow excess pressure to escape slowly and evenly down the length of the hose instead of ballooning and eventually bursting.
The ends of the hose determine what kind of hose it is really. Each end is crimped on and you'll have a male and female end. The male end screws into your 1st stage and comes in three basic thread sizes 3/8", 9/16", 1/2" which have their own uses. 3/8" and 1/2" are low pressure and 9/16" is only for high pressure so you don't mix them up. For more info on threads check out my other blog on choosing hoses. Because you have a rigid metal section at each end of the hose the soft part can often crimp and tear the outer layer so you need to use hose protectors where you can to extend the lift of your hose.
The most common 'issue' I tend to hear about is the tiny holes running down the length of hoses. These holes are a safety feature made by the manufacturer to evenly release pressure if the internal hose fails. An unfortunate side-effect of these holes is that the air trapped between the fibers of the mid layer are squeezed out and fizz through these holes for a little while at the start of a dive which some people think is a leak even though it is perfectly fine. At the beginning of the 2nd dive pressurizing your hoses can squeeze moisture in those little holes out so it looks like the hose is sweating, again this is normal and no action is needed. If your hose continues to fizz without signs of stopping then end the dive immediately and replace the hose.
Hoses leaking at either end have a damaged or missing O-Ring. The end attached to the 1st stage only needs one O-Ring and it should be soft and rubbery, hard and brittle O-Rings crack. The other end depends on what hose it is... QD hoses have a schrader valve inside that can wear out over time but are easily changed with a tool. Regulator Hoses have an O-Ring around the internal section that can be tricky to get out without a pick but are easy to change after you've done a few. HP hoses need a swivel, a small hollow pin with a tiny O-Ring around each end, this allows your gauges to swivel and turn on the hose. Transmitters are like HP hoses in that they need an O-Ring when screwing directly into a 1st stage but need a swivel when screwing into a HP hose.
Rubber hoses crack over time due to a mix of sunlight, bending, contaminants in the water and just time. There is nothing you can do for a cracking hose, it simply just needs replacing. You can help to prevent a cracking hose by fitting hose protectors, storing your hoses as straight as possible and washing hoses in fresh water after every dive before drying them for storage.