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Sunday, 17 February 2019

Hose clamps - an important lesson

An important lesson we learnt early is the difference between hose clamp types. There are really only a couple of different hose clamp types used in the leisure boating industry and these are usually the worm drive strap type hose clamp.

Below pressed band worm drive strap type hose clamp

Pressed band hose clamps, the bottom clamp has done several seasons and is as good as new

One hose clamp that I have continually seen fail is the perforated hose clamp. All of our previous boats have had several failing perforated hose clamps. These are easy to identify, the thread on the strap is a series of small slots perforating through the strap. In most cases the strap material is thinner and from what we have seen will fail easily due to small amounts of crevice corrosion or they have been known to crack at a perforation over a period of time.

Below a perforated hose clamp.
Not far from failure, not as bad as some we have come across, but not good none the less

We had the stern tube seal a step from total failure, one hose clamp had failed totally and its pair had severe crevice corrosion. After finding this we went on a mission inspecting all the hose clamps on either end of a hose. Then we started to replace all the clamps used on items below the water line that keep the sea water out. Once we started we soon realized just how many hose clamps are used. We then started to replace the clamps on the pressure water system, and again there was a significant number. Even now several years later every now and then I will come across a perforated hose clamp failing or not far from it. Usually these are tucked away in some hard to reach place, making them double trouble to replace if they fail on passage.

Another problem I have found with perforated clamps used on hoses in the engine room. I am not sure whether its due to the heat, but on several occasions the hose material can be seen to be squeezed through the perforation slots. The flow on effect is a reduction in the efficiency of the clamp pressure.

This time the perforated hose clamp hasn't failed due to crevice corrosion, it just wasn't up to the job

Unfortunately price and profit margins are the reason we are supplied with inferior quality hose clamps when we purchase new equipment in kit form. The perforated hose clamp is cheaper to manufacture so most equipment suppliers will ship the new part with these types of clamps. Unless you’re really stuck, get pressed band hose clamps; they are made of thicker material and are usually able to withstand minor crevice corrosion without failing.

Another pit fall to be aware of is the use of automotive hose clamps, while these are sold as being stainless steel a lot of the time the screw (worm driver) is still mild steel and will rust out in quick time when used in the moist salty environment of a boat.

However, it’s not just on board these hose clamps can be a problem. We have seen a dock full of fire hoses where the nozzles are held on with these perforated hose clamps. The worry is if there is actually a fire. Instead of being able to use the nozzle as a shield (water curtain) or project the water all you will be left with is an open end once the water pressure is turned on. The nozzle will be long gone a projectile, let’s hope it doesn’t knock someone out when it lands after taking flight.

This is one of several failing hose clamps used to keep on the high pressure fire hose nozzle
As seen on the hose clamp above even the worm drive screw is rusting, possibly the band was stamped as stainless steel but the screw is mild steel. We have seen this on several occasions, these are usually clamps targeted to the automotive market and sold as stainless steel band clamps.

Before committing to purchasing a number of clamps take along your magnet and test the clamps for steel content, then buy one and over the next week have it in and out of sea water to test to see if there are any rust spots or reaction before buying more.

A good heavy duty hose clamp, great for larger diameter hoses like exhaust hoses, no worm drive screw to fail.



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