Valve applications in industrial sectors

ARGO-HYTOS has been manufacturing hydraulic valves for use in potentially explosive atmospheres (Ex valves for short) for almost ten years. The valves are used to control the hydraulic circuits of mining machines (group I), equipment in the chemical and petrochemical industries where the explosive atmosphere consists of gases (group II or IIG), and in lime kilns, cement plants, mills and textile industries where the explosive atmosphere consists of dust or flammable fibres (group III or IID).

Zonal use of valves

The valves have a protection rating of EPL b. They are therefore designed for use in zones 1 and 2 of potentially explosive atmospheres consisting of gasses and zones 21 and 22 cosisting of dust. In underground mine environments, the valves are intended for use on category M2 equipment, which is shut down when an explosive atmosphere occurs.

Three types of Ex valve design

There are three basic solenoid operated Ex valves designs available on the market.
In the first group are spool directional control valves with body and connection pattern DN 06 according to ISO 4401, including proportionally controlled.
The second group consists of spool valves of sizes DN 10, DN 16 and DN 25 with a pilot valve of DN 06 for controlling large volume flows up to 600 l/min.
The third group includes valves designed to be screwed into blocks. These are screw-in cartridge spool valves, poppet valves and proportional pressure reducing valves.
Each valve consists of an electrical part, the solenoid control coil, and a mechanical part that includes the solenoid control system and the hydraulic part of the valve.

ExProof protection of electrical parts

The basic type of protection for the solenoid coil is the encapsulation of the coil with insulating material (protection type "m" EN 60079-18). The terminal block for the electrical connection of the coil and the cable gland are certified "e" (EN 60079-7). If AC power is used, a diode rectifier, also encapsulated in insulating material, is built into the terminal block. Therefore, Ex valves with AC coil supply are only supplied with a connected, non-removable cable.
The "m" protection method used is comparable in level to the fixed closed "d" (EN 60079-1) and provides the user with advantages when wiring the valve. Neither a cable gland with "d" certification or a restraining mechanism against cable displacement by gas pressure are required.
For explosive atmospheres consisting of dust, protection by a fixed „t“ (EN 60079-31) closure is used.

ExProof Coil certifications

The coils have ATEX certification according to European Directive 2014/34/EU, internationally valid IECEx certification according to IEC standards as well as some local certifications, e.g. IECEx certification for Australia and New Zealand or EAC certification according to TS 012 / 2011 valid for the Eurasian Economic Union (EAEU), i.e. for the Russian Federation, Belarus, Armenia, Kazakhstan and Kyrgyzstan.

Valves temperature classes in ExProof enviroment

In addition to the different DC and AC supply voltage ratings of the coils, two power ranges are available, 10W and 18W. The power rating of the coil is related to the maximum surface temperature of the coils in temperature classes. Valves with a 10W coil can be used in temperature classes T4 (135 °C), T5 (100 °C) or T6 (85 °C) provided the specified electrical parameters of power supply, ambient temperature and maximum liquid temperature (70°C) are not exceeded. The 18W coil emits higher heat loss and can only be used in the T4 class. The higher power 18 W are use for control of spool valves with spool position lock and proportional valves T4.

Additional emergency feature

The valves can be equipped with a manual emergency control that allows the spool / cone to be repositioned in the event of a solenoid failure or power failure up to 25 bar in the control system. Two designs are available, pin operated and with detent assembly.
A solenoid operated directional control valve with a built-in manual lever mechanism, allows manual valve control up to 100 bar pressure in the "T" port. The mechanism does not affect the valve function when operated by solenoids.

Conclusion

Experience from applications in various industries and countries around the world confirms that the valves provide sufficient protection against explosion initiation, are functionally reliable, corrosion resistant and resistant to mechanical damage even under severe mine operating conditions.