HYDAC kept its ear to the ground and came up with PDRC/WKC pilot valves to overcome areas of machinery complaint in the field.

Comments such as the following are regularly bandied around: 

"Machine (even the big ones) must respond directly!"

"I need components that do not have to be calibrated again in the production line."

"Small machines for narrow work areas that can be automated are needed."

"I need a machine that works reliably in all environmental conditions."

"Safety is a top priority."

To overcome these issues, the following is required, according to a HYDAC spokesperson:

-dynamic and precise conversion of electronic to hydraulic signals, which makes for precise movement at all operating points (even with pilot flow demand of >10L/min);

-precise and repeatable control for "fine" joystick movements and controlled, automated sequences;

-valves with QR code for easy calibration (optional);

-valves suitable as an actuator in control loop with displacement and angle control;

-miniaturisation of pilot control circuits;

-good control behaviour over a wide temperature range;

-EH pilot valves with low leakage to ensure controlled drop of the boom for a sufficient period in the event of a fault; and

-contamination-resistant components.

HYDAC's solution: PDRC/WKC pilot valves

HYDAC meets these requirements with its PDRC/WKC pilot valves.

According to the spokesperson, PDRC/WKC pilot valves feature high power density in compact design; high quality plain bearing for low hysteresis; and various connection options such as Deutsch, Junior Timer (axial), and Deutsch, Junior Timer (radial).

One coil, one pitch - different valve options

PDRC04T30D

Specifications for the PDRC04T30D are as follows:

Pmax: (in) = 60 bar

Pmax: (control) = 32 bar

Qmax = 4L/min

The PDRC04T30D is known for its robust design and suitability for ready use in existing applications (characteristic, hysteresis, dither).

PDRC05S30A-14

PDRC05S30A-14 specifications are as follows:

Pmax: (in) = 60 bar

Pmax: (control) = 35 bar

Qmax = 10L/min (20L/min)

The PDRC05S30A-14 is known for its extremely high-power density and highly effective flow force compensation.

WKC05S30

Specifications of the WKC05S30 are as follows:

Pmax: (in) = 60 bar

Qmax = 18L/min 

The WKC05S30 is known for its high switching capacity and compact and robust design.

Target: dynamics in the main spool valve

There is a requirement to fill and drain a pressure chamber in a main spool faster and more precisely than conventional valves. This requires high system dynamics with simultaneous, precise control, even at high viscosity (cold oil).

Requirements:

This requires fast response time of the pilot system, keeping in mind that valves with low inductance achieve high dynamics.

Especially for larger machines with large main spool valves, high and simultaneously controlled volume flows are required to achieve high system dynamics.

Dynamic controlled handling of the main spool valve by PDRC

Example: dynamic filling of the pressure chamber in the MCV to 28 bar. 

Conventional valve

The pilot valve first opens completely to the saturation point. Flow forces prevent complete control, leading to a temporary loss of control. 

PDCR with patented flow force compensation

The pilot valve opens completely, flow forces are controlled, which results in controlled regulation at even higher volume flows, no overshoot and higher dynamics occurs. 

Patented flow force control through use of small magnets with high dynamics.

Dynamic control

How did HYDAC manage that?

Virtual hook:

From the saturation point, the direct-controlled PDRC05S30A is temporarily pilot-controlled and controls the flow forces. 

Leakage and control mode remains low because pilot control is only active from the saturation point onwards. 

This results in reliable control of flow forces at critical operating points.

Extremely precise control

For a perfect machine response

Features include very good reversal span (hysteresis in the small signal range), with low valve leakage. 

Hysteresis in the small signal range is five times smaller than with conventional valves.

In the fine control range, the output signals are the same for rising and falling current ramps.

According to the spokesperson, the ‘goal' is no delay or jams in the output signal when the drive current is finely adjusted. 

The spokesperson adds that the ‘challenge' is low reversal margin and still low leakage, leading to sufficient time to set down the boom in case of a pump failure due to low accumulator discharge. 

Extremely precise machine control 

with EH joystick or automated 

EH joystick control advantages

EH joystick control advantages include direct precise response of the machine, even with fine operation of the joystick. 

Advantages in automated control or with assistance systems include high stability of the control loop on machines with position feedback due to extremely precise control of the set point value and repeatable output values without jumps, which enable precise automation of movements. 

This results in a machine's precise reaction to fine signal changes, with low leakage at the same time and maintenance of the emergency supply by the pressure accumulator.

HYDAC's solution makes the difference

PDRC - pilot valves

HYDAC's PDRC slip-in valve solution makes a difference because it includes miniaturised solenoids that enable high valve dynamics due to low inductance; extremely good control of flow forces at all operating points due to artificially generated counter forces at high flow (patented); low hysteresis and reversal span with simultaneously low leakage even in operation duty due to special control edge design; and a grid dimension of approximately 30mm, which enables the automation of mini excavators.