Drainchem understands the science behind jetting nozzles

Apr 03, 2023

When it comes to high pressure water jetting, the quality of equipment is important, but so is making sure that the equipment is fit for purpose.

Drainchem’s Managing Director, Marshall Horne, talks to Trenchless Australasia about the importance of choosing the correct nozzle for the job. “Choosing the right nozzle is a science. The angle and number of water jets can vary from model to model,” says Horne.

“Not only that, but the internal design of the flushing nozzle – the passages where the water runs through the nozzle body before the water flows out through the jets also changes.”

Horne says that the three tiers of nozzle are the simplest way to talk about quality. Tier one nozzles have the water jets drilled directly into the equipment.

“The problem with tier one is that, once the nozzle is worn out, you have to throw the whole piece away,” he says. “Tier two and three nozzles will have screw-in jets, which lets operators replace them as they wear out, while keeping the original nozzle.”

Both nozzle types have very basic hydro dynamic design and typically deliver only 30-40 per cent of pump power to the pipe. Tier three nozzles are well-designed, with inner workings that guide the flow of water directly to the jet, rather than having a single chamber like the drilled nozzles at tier one.

Number of water jets

The number of water jets – the number of times the water flow is divided – the thinner each water jet will be. “A good rule of thumb is to choose a nozzle with fewer water jets, which makes the jets you do have as thick and powerful as possible,” Horne says.

However, he does warn customers that fewer jets can clean pipes unevenly, often looking like the pipe has been roughly scoured in some sections – an effect called ‘stripping’.

“Stripping usually happens when the obstructing material is hard packed on the sides of the pipe, or if there is any drainage material in the pipe, such as loose sand or gravel,” he says.

Stripping can cause problems in the future, as CCTV inspection of assets can sometimes read strips as cracks in the pipe. For moving material in-pipe, Horne says that fewer jets are still more effective compared to using many smaller water jets. “To optimise work, operators should be sure to have access to both options on the job, as nozzles with more water jets are better designed for pipes that require 360˚ cleaning,” he says.

Water jet angles

Nozzles are separated into three categories, based on the angle of their water jets. 0–12-degree rear thrusting jets are designed to move material in the pipe. “The lower the angle, the more efficiently material will be transported in the pipe,” says Horne.

At a lower angle, the distance between the nozzle’s jet and the pipe wall is greater. If the inner structure of the cleaning nozzle is optimised with a water-conducting design, it will keep the jets together behind the nozzle for longer stretches. 

“This means that operators can work with lower jet angles and still clean all the way out to the pipe wall,” Horne says. “But nozzles with poor internal design are not going to cut it, especially for larger pipe diameters.”

13–30-degree rear thrusting jets, normally called universal cleaning nozzles, often have more rear thrusting jets that sit at multiple angles. “They can typically move material in-pipe if there is not too much, and they’re characterised by efficiency,” says Horne. “Universal cleaning nozzles are also able to clean the inner pipe wall effectively, as long as the material is not too hard or greasy.”

31–90-degree rear thrusting jets should be used exclusively for pipe wall washing or descaling. 

Examples of these are rotary nozzles and bombs, flounders or grenade type nozzles – where 50 per cent of the jets have an angle of up to 85 degrees. These are intended for pipe wall cleaning and descaling operations. 

“These types of nozzles are not designed to move large amounts of material in pipe,” says Horne. “If the pipe contains a large amount of material, operators first need to clean out the material with a more efficient 0 to 12-degree cleaning nozzle.”

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