Testing the effectiveness of release valves under intensive dynamic load to the leg

overload caused by rock bursts or bumps. Due to an essential role in
ensuring safety in the working, an application of a release valve is
conditioned by a positive yield test results of a leg equipped with
such a valve. A method of leg yield testing, used in Poland, enables
a complex determination of an impact of not only a release valve
but also of the parameters of the hydraulic leg, dete
stiffness such as for example a volume of the under
space, which has an impact on an observed pressure
The subject of this publication covers cognitive tests oriented onto a
determination of an impact of a release valve exc
pressure changes observed in the leg. The results of the efficiency
tests of spring valves (Stoiński, 2018) on a rammer are discussed.
The difference between the maximum pressure in the under
area of the leg with the release valve and the maximum pressure
generated by the same dynamic load in the leg without this valve
was the measure of the valve operation's effectiveness.
Dynamic load, realized on a rammer, is characterized by a longer
increase time than in the case of dynamic load
roof support unit from the floor. The time process of the force in the
leg is then characterized by a short load rising time
increment factor – Kd and the average load growth rate
Referring to that aspect, the features of a release valve were
analyzed in relation to the parameters characterizing dynamic load
acting on a powered roof support unit from the floor.
Parameters characterizing the effectiveness of the release valve, i.e.
change in the leg load increment index –∆Kd
of load increase –∆wpn were defined. The test stand for generating
the load of such parameters using the explosive method is
described. Comparison of effects of the dynamic load generated by
firing the same mass and the same type of explosive on a hydraulic
leg with a release valve and the leg without this valve was the test
objective.
The effectiveness of the spring valve and two gas valves are
analyzed. It was found that despite a very short load rising time, the
release valve reduces the load acting on the leg. The positive values
of the ∆Kd and ∆wp,n indices are the evidence.