Electro hydraulic proportional directional flow valve

Electro hydraulic proportional flow directional control valve: precise control solution for 10-250L/min under 25MPa high pressure

In modern hydraulic systems, directional control and flow regulation often require two independent valve components - the directional valve controls the opening and closing of the oil circuit, and the throttle valve or speed regulating valve controls the flow rate. This split type scheme not only occupies a large space and has complex pipelines, but also makes it difficult to achieve smooth acceleration/deceleration control that is deeply integrated with the electronic control system. The emergence of electro-hydraulic proportional technology has changed this situation: by changing the magnitude of the input current, the same valve core can switch the direction of oil flow and continuously adjust the flow rate, providing a structurally compact, responsive, and easy to remotely control solution for injection molding machines, presses, walking machinery, test benches, and other equipment.

The series of electro-hydraulic proportional flow directional control valves (10-250 L/min, maximum working pressure 25 MPa) introduced in this article are industrial grade products designed based on the above concept. This series includes direct acting 01 specification and pilot operated 03, 04, 06 specifications, driven by DC proportional solenoid, with built-in manual adjustment screw, supporting internal or external oil discharge, and optional pressure compensation valve kit to achieve load independent flow control. The following will provide a comprehensive technical analysis of the valve from multiple dimensions, including technical specifications, model codes, structural principles, performance curves, installation and use, and pressure compensation kits.

Product Overview and Technical Features

1.1 Core Design Philosophy

This series of valves is essentially a four-way proportional valve that can simultaneously complete direction switching and flow control. The traditional switch type electromagnetic directional valve only has two states: "on" and "off", while the proportional solenoid of the proportional valve can generate an electromagnetic force proportional to the input current, thereby pushing the valve core to overcome the spring force and move to a certain intermediate position, opening the corresponding throttle area. When the direction of input current changes, the proportional electromagnet on the other side works to switch the direction of oil flow.

The biggest advantage of this design is that it replaces the combination of "directional valve+throttle valve" with one valve, simplifying the hydraulic circuit; Realize shock free acceleration and deceleration through ramp current signals to avoid hydraulic shock; Support remote electrical control for easy integration into PLC or CNC systems.

1.2 Series division and applicable traffic

According to different diameters and rated flow rates, this series is divided into four specifications:

Specification, model, prefix, rated flow rate (L/min), maximum flow rate (L/min), structural form

01 ESD-G01 10/20 25 Direct Acting

03 ESD-G03 40/80 100 Pilot operated

04 ESD-G04 140 140 Pilot operated

06 ESD-G06 250 250 Pilot operated

The rated flow rate is measured under the condition of a pressure drop of 1.0 MPa (approximately 10 kgf/cm ²) for P → A and P → B. Users can choose the appropriate specifications based on the required speed of the actuator to avoid excessive pressure loss or decreased control accuracy.

1.3 Work pressure and environmental adaptability

The maximum working pressure for all specifications is 25 MPa (255 kgf/cm ²), which can meet the pressure rating of most industrial hydraulic systems. T-port allows for back pressure: 2.5 MPa for internal discharge type and up to 21 MPa (214 kgf/cm ²) for external discharge type, providing flexible options for pilot stage oil discharge in complex circuits.

Temperature range of hydraulic oil used: -20 to+70 ℃; Range of kinematic viscosity: 12-400 mm ²/s, recommended viscosity 15-60 mm ²/s. It is recommended to control the pollution level at NAS level 9 or higher (ISO 4406 18/15), and it is recommended to install a return oil filter with an absolute filtration accuracy of 8 μ m.

Detailed specification parameters

2.1 Electromagnetics and Dynamic Performance

Rated current: 850 mA (all specifications are consistent)

Coil resistance: 20 Ω (at 20 ℃)

Lag: ≤ 5% (when using Nachi Fujikoshi dedicated amplifier)

Response time (oil supply pressure 14 MPa, oil temperature 40 ℃, viscosity 40 mm ²/s):

ESD-G01：0.04 s

ESD-G03：0.05 s

ESD-G04：0.08 s

ESD-G06：0.10 s

Response time is defined as the time required from zero input to rated flow rate. For systems that require rapid pressure building or emergency braking, the 40 millisecond response of 01 specification is already excellent; The 100 milliseconds of the 06 specification is also reasonable for high flow valves.

2.2 Pilot pressure and flow requirements (for specifications 03/04/06)

Pilot operated valves require sufficiently high pilot pressure to ensure reliable switching and adjustment of the valve core:

Pilot pressure: at least 1.0 MPa (10 kgf/cm ²), which is the pressure difference between the pilot port and the return port (or drain port).

Pilot flow rate:

G03: At least 2 L/min

G04: At least 3 L/min

G06: At least 5 L/min

If the pilot pressure exceeds 9 MPa (92 kgf/cm ²), it is recommended to install a modular pressure reducing valve (such as OG-G01-P1-21) at the P port and set the pilot pressure to around 2 MPa to avoid excessive hydraulic force on the proportional solenoid.

2.3 Weight

ESD-G01：2.2 kg

ESD-G03：7.2 kg

ESD-G04：9.2 kg

ESD-G06：15.0 kg

Model Code and Selection Guide

The basic structure of the model coding rule (taking the illustration in the document as an example) is:

ESD - G 03 - * * * * * * * * * * - 12

Meaning of each field:

ESD: Product Series Code

G: Equipped with modular pilot pressure reducing valve (height increased by 40mm) or specific configuration identification

03: Specification code (01/03/04/06)

Middle section: valve core form, spring configuration, flow regulation range, etc. (refer to the selection table for details)

12: Design Number

The document provides a slide valve type table (Table 1), which lists the hydraulic circuit symbols corresponding to different valve cores, such as C5, C6, etc. Users should choose the appropriate valve core model based on the required slide valve function of the actuator (such as center closing, center floating, etc.).

Attachment and option identification:

Auxiliary symbol "G": indicates that a modular pilot pressure reducing valve has been installed, and the total height of the valve will increase by 40 mm.

The installation surface complies with ISO 4401 standard:

ESD-G01：ISO 4401-03-02-0-94

ESD-G03：ISO 4401-05-0-05

ESD-G04：ISO 4401-07-06-0-05

ESD-G06：ISO 4401-08-07-0-05

This means that the series of valves can be directly installed on any base plate that meets the same ISO standards, with good interchangeability.

Structural composition and sectional diagram

4.1 ESD-G01 Direct Acting Structure

The core components of a direct acting valve include:

Valve Body

Spool valve core

Retainer

Spring (Spring)

Proportional solenoid with coil

Multiple O-rings (used for various sealing parts)

Seal ring

When the proportional electromagnetic iron on one side is energized, the electromagnetic force directly pushes the valve core to move, compressing the spring on the other side. The displacement of the valve core is proportional to the magnitude of the current, thereby controlling the opening of the throttle port. Due to the absence of a pilot stage, the direct acting valve responds faster, but the controllable flow rate is limited by the electromagnetic thrust, resulting in a maximum flow rate of only 25 L/min for the 01 specification.

4.2 ESD-G03/G04/G06 Pilot Structure

The pilot operated valve adds a pilot spool and pilot stage spring outside the main stage. The proportional electromagnet pushes the pilot valve core, controlling the flow of pilot oil into the chambers at both ends of the main valve core, creating a pressure difference to drive the movement of the main valve core. This two-stage amplification structure enables low-power electromagnets to control high flow main valves.

The sectional view shows that the pilot operated valve includes:

Main valve body

Main valve core (Spool)

Pilot spool

Pilot spring and spring seat

Manual adjusting screw

Various seals (O-rings)

The manual adjustment screw is located on one side of the pilot stage, and clockwise rotation can force the valve core to the working position, which is used for initial adjustment or manual operation in emergency situations such as power outage. During normal use, the adjusting screw should be fully retracted counterclockwise.

4.3 Changes in Pilot Oil and Oil Discharge Method

The document provides detailed methods for modifying the pilot/drain system. Users can configure the valve according to their circuit needs as follows:

Internal pilot: The pilot oil comes from the P port and is suitable for systems where there is always pressure at the P port.

External pilot: The pilot oil comes from an independent X port (or Pp port), suitable for systems with large pressure fluctuations at the P port or requiring low-pressure start-up.

Internal drain: The pilot drain oil returns to the T port, which is simple and convenient, but the back pressure at the T port should not be too high.

External drain: The pilot drain oil is directly returned to the tank (DR port), allowing the T port to withstand high back pressure.

The usual way to change the oil circuit connection is by screwing in or out certain Hexagon socket head plugs. For example, for G03, changing the inner pilot to the outer pilot requires removing the plug from position A, while changing the outer pilot to the inner pilot requires inserting the plug. These operations require disassembling the end cover of the valve and replacing the corresponding sealing ring.

Key points for installation and use

5.1 Exhaust

The air dissolved in hydraulic oil will precipitate under high temperature and pressure, affecting control stability. Before starting, the air vent plug on the valve must be loosened and tightened after the air is discharged and pure oil flows out. Special note in the document: There is an M4 fastening screw on the coil cover plate. If you need to change the direction of the exhaust port, you can loosen the screw and rotate the cover plate. After completing the exhaust, tighten it again.

5.2 T-port piping

For pilot operated valves (G03/G04/G06), the T port (T port of the pilot valve) must be filled with oil and no air chamber is allowed. When piping, ensure that the return oil pipeline is submerged below the oil tank level and avoid sharing with the high-pressure return oil pipeline, which may cause back pressure impact.

5.3 Valve installation direction

In order to prevent the movement of the valve core from being affected by gravity, the valve should be installed horizontally (spool axis line horizontal). If vertical installation is necessary, the manufacturer should be consulted to see if it is allowed and if it is necessary to adjust the spring preload force.

5.4 Combination use with pressure compensation valve

When the actuator load changes significantly, the output flow rate of a conventional proportional valve will vary with the load pressure (similar to the characteristics of a throttle valve). In order to achieve load independent flow control, it is necessary to cooperate with a pressure compensation valve. This series provides a dedicated pressure compensation valve kit (JHF series) that can be installed between the valve and the base plate or integrated into the pipeline to maintain a constant pressure difference at the valve port, thereby allowing the flow rate to be proportional only to the input current.

The specific parameters and installation methods of the pressure compensation valve will be described separately in the following text.

5.5 Additional measures under special working conditions

High brake pressure system: For example, when a hydraulic motor brakes quickly, a high-pressure impact will be generated on the return oil side. At this time, counter balance valves should be installed on both sides of the motor.

Vertical oil cylinder: When using a single rod cylinder and the piston rod extends too quickly during downward movement, a balance valve should be installed on the return side to prevent overspeed and falling.

High pilot pressure: If the pilot pressure exceeds 9 MPa, a P-port pressure reducing valve (such as OG-G01-P1-21) must be installed and set to 2 MPa.

5.6 Installation bolts and tightening torque

The specifications and tightening torque of the installation bolts attached to the valve are as follows:

Model, bolt specification, quantity, tightening torque N · m (kgf · cm)

ESD-G01 M5×45 4 5～7 (51～71)

ESD-G03 M6×35 4 10～13 (102～133)

ESD-G04 M6×45 2 10～13 (102～133)

ESD-G06 M12 × 60 6 45-55 (460-560) or 60-70 (610-715)

Attention: G06 provides two sets of torque values, which may correspond to different materials or sealing methods. The actual markings should prevail.

Performance curve analysis

6.1 Input current flow characteristics

The document provides the input current flow characteristic curve measured under the conditions of pressure drop Δ P=1.0 MPa and oil viscosity of 32 mm ²/s. Curve display:

As the current increases from 0 mA to the rated current of 850 mA, the flow rate gradually increases from zero to the rated value.

The curve exhibits a certain degree of nonlinearity, especially in the low current region (dead zone). Usually, amplifiers provide a "dead zone compensation" function to improve the accuracy of small signal control.

The lag is less than 5%, which means that under the same current, there is little difference in flow rate when approaching from two different directions. This is sufficient for open-loop proportional control systems, but for closed-loop precise control, it is recommended to use proportional valves with displacement feedback.

From the curves of ESD-G04 and G06, it can be seen that the flow regulation range is wide and has good linearity in the middle section. Users can set acceleration/deceleration times through a ramp generator (usually integrated into an amplifier) to achieve smooth speed changes.

6.2 Pressure flow characteristics

The pressure flow characteristic curve shows the maximum flow rate that the valve can pass through under different valve port pressure differentials. When the pressure difference increases, the flow rate also increases, but it is limited by the maximum opening area of the valve port and eventually tends to saturation. These data are crucial for system designers to calculate pressure loss and determine the set pressure of the pump.

For example, when 250 L/min is required, if ESD-G06 is used, the corresponding valve port pressure difference is about 1.0-1.2 MPa. If the system allows for higher pressure loss, the valve diameter can be reduced to save costs, but the heat generation must be accounted for.

Pressure compensation valve kit (JHF series)

7.1 Why is pressure compensation necessary

The ordinary proportional directional valve is essentially an adjustable flow port, and its flow formula is Q=K ⋅ A ⋅ Δ P

Q=K⋅A⋅ ΔP， Where Δ P is the pressure difference before and after the valve port. When the load changes, Δ P changes accordingly, and even if the valve core opening area A remains unchanged, the flow rate will fluctuate. In hydraulic systems, this can cause the actuator speed to vary with changes in load, affecting machining accuracy or motion stability.

A pressure compensation valve (also known as a flow control valve or differential pressure reducing valve) is connected in series before the proportional valve, which can automatically adjust its own throttle port to maintain a constant pressure difference at the valve port of the proportional valve (e.g. 1.0 MPa). In this way, the flow rate is only proportional to the opening area of the proportional valve, thereby achieving load independent flow control.

7.2 JHF series specifications

The document provides four types of pressure compensation valve kit models:

Model Maximum pressure MPa Compensation pressure difference MPa Maximum flow L/min Weight kg

JHF-01027 21 1.0 27 1.5

JHF-03040(E) 25 0.6 40 4.7

JHF-03080(E) 25 1.4 80 4.7

JHF-06170(E) 21 0.8 170 5.0

The "E" in the model indicates an external pilot type, and without an E, it is an internal pilot type. The pilot oil of the internal pilot type comes from the P port; The external pilot type requires the introduction of pilot oil from the external Pp port, which is suitable for situations where the compensating valve and proportional valve need to be supplied separately.

Important note: When using the pressure compensation kit, it is necessary to use an external pilot type ESD valve (i.e. with an external pilot option in the model). This is because the compensating valve will change the pressure characteristics of the P port of the main valve, and the internal pilot may not be able to obtain stable pilot pressure.

7.3 Installation and piping

The pressure compensation valve kit is usually installed in a stacked or tubular manner between the proportional valve and the base plate. The installation bolts need to be purchased separately, please refer to the bolt list on pages D-93 to D-95 in the document. The external dimension diagram shows the installation dimensions of JHF-01027 and JHF-06170 (E), including oil port position, bolt hole spacing, etc. When designing the integrated block, the installation surface must be machined strictly according to the dimensions shown in the diagram.

Selection of compensating pressure difference: For systems that require low pressure loss, JHF-03040 (E) with a compensating pressure difference of 0.6 MPa can be selected; For applications that require higher response speed or more stable control, JHF-03080 (E) with a pressure difference of 1.4 MPa can be selected. A larger compensation pressure difference helps to overcome the frictional force and hydraulic force of the valve core, but it will increase the power loss of the system.

Seals and repair kits

8.1 ESD-G01 Sealing Kit

Model: JDS-G01-1A

Includes parts: O-ring AS568-012 (4 pieces), AS568-019 (2 pieces), NBR-90 P22 (2 pieces), AS568-016 (2 pieces), NBR-90 P7 (2 pieces), S-25 (2 pieces), NBR-70-1 P20 (2 pieces), sealing ring CW1000F02 (1 piece). The material hardness meets the JIS B2401 standard.

8.2 Pilot stage sealing kit (for G03/G04)

Kit models: JHS-G03 and JHS-G04

It includes various O-rings for pilot valve core, screw plug and other parts, such as NBR-90 P12, P9, P28, P10A, etc. When replacing, be sure to refer to the parts list and exploded view to avoid installing in the wrong position, which may cause leakage or valve core jamming.

8.3 Pilot stage sealing kit (for G06)

Kit model: JHS-G06

Includes O-rings NBR-90 P28 (4 pieces), P20 (2 pieces), G45 (2 pieces), P10 (2 pieces), P8 (3 pieces). The sealing structure of G06 is slightly different from other specifications and cannot be mixed.

When disassembling the valve for maintenance or changing the pilot/oil discharge method, all removed O-rings should be replaced to ensure sealing reliability.

Typical application scenarios

Injection molding machine: Control the speed switching and pressure relief of the injection cylinder, and use slope signals to achieve graded control of injection speed.

Press: Control the speed and direction of the slider's rapid descent, pressing, holding, and return, and cooperate with the pressure compensation valve to overcome the influence of unbalanced load.

Test bench: When testing the performance of hydraulic components, it is necessary to accurately adjust the flow rate and frequently change directions. The combination of proportional valves and PLC can achieve automated testing cycles.

Mobile machinery (such as forklifts and excavators): remote electronic proportional control, simplifying the mechanical linkage mechanism of the cab control lever.

Wind power variable pitch system: Real time adjustment of blade angle based on wind speed, requiring fast response and long-term operation in vibration environment.