Process Characteristics Of Hydraulic Legs Equipped With Safety Valves At Dynamic Load Caused By A Mining Tremor

• Published in: Archives of mining sciences = Archiwum górnictwa 2015-06, Vol.60 (2), p.595-612
• Main Author: Pytlik, Andrzej
• Format: Article
• Language: English
• Subjects: bypass valves; capacity; hydraulic legs; individual roof support; obudowa indywidualna; obudowa zmechanizowana; powered roof support; przepustowość; safety valves; stojaki hydrauliczne; zawory bezpieczeństwa; zawory przelewowe
• ISSN: 1689-0469; 0860-7001; 1689-0469
• DOI: 10.1515/amsc-2015-0039

The article presents process characteristics of hydraulic legs, a powered roof support and an individual roof support that are equipped with pressure relief valves and additional safety valves protecting the legs against dynamic loads caused by mining tremors. A two-telescopic hydraulic leg ϕ330 type was tested using dynamic pile testing, equipped with a valve bank with pressure relief valve and an additional safety valve. The tests included the following models of safety valves described in references (Gwiazda, 1997; Irresberger et al., 2008): Using pressure charts in time function it is possible to determine how fast the amplitudes of pressure increase with the height of a ram increase, thereby, kinetic energy of ram’s stroke and momentum impacting the leg equipped with the valve. Maximum pressure in the leg with the slide-piston valve raised to 64 MPa (with impact mass drop at = 0.25 m) up to 129 MPa ( = 0.3 m) i.e. by 100%. Pressure increase to was noted during a test of the slide-piston leg equipped with the valve and with a drop of = 0.5 m This poses a great hazard that can destroy the valve and therefore cause a loss of load-bearing capacity. Conducted research of SHC hydraulic legs of an individual roof support showed that (Pytlik & Pacześniowski, 2012; Pytlik & Rabsztyn, 2011) quick relief valves had higher efficiency than standard valves mounted in SHC legs, which resulted in lower pressure in the leg by 7 MPa. It has an essential importance for stability of leg’s cylinder and its sealing. The test of the leg with a valve battery was based on its dynamic load impacted by a ram (impact mass) of = 4,000 kg relieved at the leg placed between a cross-bar of = 3,300 kg and post’s foundation. Recording of pressure of the fluid in its space under piston was made with sampling frequency of 9.6 kHz, Moreover, the research also included test of the same type of SHC leg with BZG-2FS battery (equipped with gas spring) using ram’s mass of = 2,0000 kg and the cross-bass of = 6,600 kg. The leg transferred the load, stroke type, of = 29,5 kJ kinetic energy without any damages. A time-lapse analysis of photos showing the opening moment of the safety valve indicated that its opening had taken place 8 ms after the moment when the leg was impacted and indicated propagation of the hydraulic fluid stream’s front with maximum velocity of about 60 m/s, and maximum momentary intensity of fluid flowing through a bypass valve amounted to = 683 l/min. The tests of work char