Waterjet Cutting News Tech Tips

JetTalk: Where did the pressure go?

You are about to carry out a cutting project. All settings on your machine are in order and you have also installed brand new nozzle and orifice.

Next, you start the pump but somehow, you are not getting enough pressure at the cutting nozzle. Meanwhile, you re-check the settings and scan through the high pressure line – and can’t detect any leaks.

Where did the pressure go?

This is indeed a common question I hear from waterjet operators (especially new operators). However, this serious concern can be easily addressed.

In every waterjet cutting machine, the high pressure pump is equipped with a safety valve, also known as a ‘Dump Valve’. The function of the safety valve is to maintain the pressure in the high pressure line during the cutting process and to release it when the process is complete.

As you know, the safety valve consists of an On/Off valve kit and in most cases, it is identical to the cutting head’s On/Off valve assembly. In circumstances where the On/Off valve needle assembly is worn out in the safety valve, the high pressure water will start to leak from the valve during the cutting process and hence, the pressure drops. 

Although the leakage is internal and cannot be seen externally, it can create doubts in the operator’s mind and raise various concerns on the possible causes of the problem.


Therefore, the simple solution to stop the leakage is to replace the worn out On/Off valve needle assembly and the pressure at the cutting nozzle will return back to normal.

A good tip to remember when you find no major leakages from the high pressure line, and the nozzle and orifice are in good condition, is to check the safety valve kit. This will save you a great amount of time that you could spend on trying to figure out other possible causes.


By Ajay Thanki,  GMA Middle East
Certified Technician for Waterjet Operation and Maintenance SSPC Coating Inspector

*Note: These recommendations are to be implemented at the user’s discretion and deemed fit for their operating environment. In no event will GMA be responsible for expected performance or damages of any nature whatsoever resulting from the use of or reliance upon information presented here.