THE WATER HAMMER EFFECT: NEW TECNOLOGIES TO AVOID IT IN HYDRAULIC PRESSES

This article analyse the water hammer effect and how to avoid it in hydraulic presses. By definition, the “water hammer” effect (Nikolai Zhulowski pulse) is a pressure wave that is created when a fluid is forced to change speed suddenly and this surge or wave moves at the speed of sound through a pipeline system. The water hammer effect damages machines because it causes vibrations, sudden pressure increases and forces that to act on piping and mechanisms. Also the noise level increases badly.
Since time immemorial, people have known the destructive effects of a quick, sharp pulse in a fluid, because a sudden surge produces forces far greater than those produced alone. Hydraulic presses work by making oil flow at pressure to one or several cylinders that, when filled, drive the pistons that move the slide supporting the die. Evidently, modern presses need to have many different ways of working and move at high speed, and as a result the flow of oil is never calm and stable. The complexity of the tubing, its pathway, pump and valve operations, accelerating and braking to programme work cycles etc., mean that this flow is frequently activated and then interrupted.

Fundamental Design Concepts in order to avoid the Water Hammer Effect in Hydraulic Presses

Fagor Arrasate adds many concepts to its hydraulic presses in order to avoid the water hammer effect. As the machine has a useful life of several decades and conditions are unpredictable, it is important to minimize the effect and any consequences if it does occur. To achieve this, the following measures are taken:
• Hoses or flexible tubing are used when permitted by regulations.
• Use of mechanically regulated logic elements.
• Gradual slide braking.
• Gradual decompression.
• Design of group blocks with integrated injectors.
• Correct installation of clamps and tube supports.
• To use a 3D design of the hydraulic installation in order to optimize the tube route.
• Finally, during set up, Fagor Arrasate checks the installations with a high performance SCADA so that hydraulic equipment is perfectly fitted, ensuring that the machine leaves the factory without any pressure peaks that could cause problems in the future; it is always delivered having been tested and adjusted.