Introduction to Rexroth Directional Control Valves (Germany)

Brand

REXROTH/Germany Rexroth

Application Areas

Chemical, Petroleum, Mining, Energy, Road/Rail/Marine

German Rexroth directional valves and BOSCH proportional directional valves are available in single-seat, double-seat, sleeve, and three-way configurations, each with single/double guide options. American ASCO solenoid valves mainly include: angle seat valves, solenoid valves, pneumatic components, proportional pneumatic products, and systems for microcomputer communication, such as valve islands, valve connection systems, simple multi-wire cable boards, and connectors. All ASCO products are designed and manufactured according to international standards. Their solenoid valves meet the needs of various applications, controlling different liquid and gaseous fluids, and offer a wide range of choices: flammable, explosive, or corrosive media; pressures up to 150 bar; temperatures from -50°C to 300°C; and diameters from 1/8 inch to 6 inches. Products include standard, explosion-proof, manual reset, intrinsically safe, sliding, long-life, steam/hot water, and pneumatically controlled valves. Its excellent explosion-proof performance makes it widely used in industries such as petrochemicals and power plants. Solenoid valves, including direct-acting, backflush, and pilot-operated types, can all be made in single-seat, double-seat, sleeve, three-way, and single/double-guided configurations; these are simply common names. Regarding the drive mechanism, electric regulating valves rely on a smart motor to drive an external valve stem, which in turn connects to the valve core for operation. Solenoid valves, on the other hand, use an external electromagnet to control the valve stem, which in turn connects to the valve core, driving either the pilot valve core or the main valve core, which is isolated by a valve cover and controlled by an external coil. The former is similar to electric valves, but consumes more power, and from a design perspective, leakage at the valve stem and valve cover must be considered. The latter type is more commonly referred to as a solenoid valve, relying on an external, invisible electromagnetic force to drive a well-sealed internal moving iron core. From a practical design perspective, leakage and the resulting unnecessary friction are not a concern. Advantages include small size, fast response, and convenient digital signal reception for control. Disadvantages include the current limitations of electromagnetic force control, which makes developing regulating solenoid valves difficult. Hopefully, future breakthroughs will bring improvements! The performance of Rexroth directional valves and BOSCH proportional directional valves primarily depends on dynamic response and symmetry. Assuming a square wave pulse signal is applied to the electromagnet, the time from receiving the signal to the actuator initiating action is called the signal delay time. This delay time comprises three parts: first, the time it takes for the current in the solenoid coil to gradually increase from zero to the point where the armature begins to move; second, the time it takes for the armature and valve core to move together; and third, the time it takes for the fixed container to fill and discharge from the opening of the throttle orifice and the venting of the actuator's working chamber to the start of the actuator's action. The first two parts are determined by the pulse width modulation (PWM) servo valve. The operating frequency of a PWM pneumatic servo valve is typically between tens of hertz and 20-30 hertz. To meet the requirement of fast dynamic response, the delay time should be as short as possible, generally controlled within 1-2 ms.

Rexroth directional valves and BOSCH proportional directional valves may fail when major components are damaged, preventing normal directional and reset actions, or when their main performance indicators significantly deteriorate beyond the specified number of directional changes. Solenoid valve classification: Solenoid valves come in many varieties. Based on the number of working positions and passages, they can be classified as 2-position 3-way, 2-position 4-way, 3-position 4-way, etc.; based on their reset and positioning methods, they can be classified as spring-reset, ball-position, and springless; based on the connection between the valve body and the electromagnet, they can be classified as flange connection and threaded connection; based on the structure of the electromagnet, they can be classified as dry type and wet type. Each category has AC, DC, and other forms, and requires various power supply voltages, resulting in many structural differences. 1. Classification by number of interfaces and switching positions: Interfaces refer to the inlet and outlet of various oil pipes on the valve. The inlet is usually marked as P, the return port as R or T, and the outlet as A or B. German Rexroth directional valves and BOSCH proportional directional valves are available and facilitate online maintenance. 4. Power supply conditions: 4.1 Based on the type of power supply, AC and DC solenoid valves are selected respectively. Generally, AC power is more convenient to use. 4.2 For voltage specifications, AC220V and DC24V should be preferred whenever possible.

4.3 Power supply voltage fluctuations are generally +10% to -15% for AC and ±10% for DC. If these fluctuations exceed the tolerance, voltage stabilization measures must be taken or special ordering requirements must be specified.

4.4 The rated current and power consumption should be selected according to the power supply capacity. Note that the VA value is higher during AC startup; when the capacity is insufficient, indirect-acting solenoid valves should be preferred.

5. Control Accuracy

5.1 Ordinary solenoid valves only have two positions: open and closed. For high control accuracy and stable parameters, multi-position solenoid valves should be selected; the Z3CF three-position normally open solenoid valve has three flow rates: micro-open, fully open, and closed; the ZDF-Z1/1 combined multi-functional solenoid valve has four flow rates: fully open, large open, small open, and fully open.

German Rexroth directional valves and BOSCH proportional directional valves require high cleanliness of the medium. Note the flow orifice diameter and inlet pipe diameter; BURKERT solenoid valves generally only have two-position on/off control; if conditions permit, please install a bypass pipe for easy maintenance; if water hammer occurs, the opening and closing time adjustment of the BURKERT solenoid valve should be customized. 2. Reliability: BURKERT solenoid valves are divided into normally closed and normally open types; normally closed type is generally selected, opening when energized and closing when de-energized; however, when the opening time is very long and the closing time is very short, normally open type should be selected. Life test, generally the factory is a type test item, strictly speaking, there is no professional standard for BURKERT solenoid valves in my country, so be cautious when selecting BURKERT solenoid valve manufacturers. When the action time is very short and the frequency is high, direct-acting type is generally selected, and fast series is selected for large diameter. 3. Safety: Generally, BURKERT solenoid valves are not waterproof, please select waterproof type when conditions do not permit, the factory can customize. The maximum rated nominal pressure of BURKERT solenoid valve must exceed the maximum pressure in the pipeline, otherwise the service life will be shortened or other unexpected situations will occur. For corrosive liquids, all-stainless steel models should be selected; for highly corrosive fluids, SLF (Solid Plastic King) BURKERT solenoid valves are recommended.

Our company primarily deals in European and American brands and can source brands from any European country. For example, our leading German brands include: BURKERT, DEMAG, HAWE, REXROTH, HYDAC, PILZ relays, FESTO, IFM sensors, E+H, HEIDENHAIN, P+F sensors, SICK, TURCK, and HIRSCHMANN industrial switches. German brands: Hengstler, Murr, Schmersal, Samson, EPRO (Emerson Group)

American brands: MOOG, ASCO, MAC, NUMATICS, PARKER, VICKERS, ROSS

British brands: Norgren

Italian brands: OMAL, ATOS, CAMOZZI, UNIVER, Camozzi