1. Purpose of online testing of safety valve:

Test and set the set pressure of the boiler safety valve according to the requirements of Guide for Application of Safety Valves for Utility Boilers (DL/T959-2005).

2. On line testing principle:

The opening and closing action of the spring safety valve depends on the medium pressure change at the inlet end and the spring preload to automatically open and close the valve core. When the medium pressure (internal pressure) rises to a point where the lifting force is greater than the spring preload, the valve core will automatically open against the spring preload to discharge excess medium and reduce the internal pressure. Due to the spring force, when the internal pressure drops to a safe value, the valve core will automatically close and the discharge will stop.

According to this principle, it can be assumed that when measuring or adjusting the safety valve online (also known as hot state), if an upward additional force is provided from the outside, when the sum of the medium pressure and the additional force just overcomes the spring preload, the valve core will also open, even under the offline (also known as cold state) condition without the effect of the medium, when the spring preload is overcome by the external additional force alone, the valve core can also open, Figure 1 clearly shows the balance relationship of this force.

Obviously, we can see that the conditions for opening the valve core are:

FT＝FW＋PＬ × S

Wherein: FT - spring preload

FW - external additional force

PL - medium action pressure

S - Sealing surface area of safety valve

Then the set pressure P is: P ＝ PL ＋ FW ／ S

When cold, P=FW ／ S

Obviously, if the additional external force FW can be accurately measured,

Based on the known spool area S and system working pressure,

The set pressure P of the safety valve can be easily obtained.

This is the design basis and principle of safety valve online testing technology.

3. System composition:

The online safety valve test bench consists of three parts: mechanical fixture, hydraulic power unit and data acquisition and processing unit. They are relatively independent of each other. Two 10m long hydraulic hoses and two 10m long five core shielded cables form a complete safety valve test system.

4. Mechanical clamp:

Ensure the clamping and positioning of the safety valve to be tested, and provide an environment for applying external force to the hydraulic power unit, Shineeast adopts a combined structure for clamp, which is very convenient for disassembly.