Proportional, or electro-proportional valves, provide infinitely variable control of flow, pressure, or direction, in response to a electric input signal.
There are four basic types of Comatrol proportional valves:
- Flow control valves
- Pressure reducing/relieving valves
- Pressure relief valves
- Directional control valves
Comatrol solenoid valves are PLUS+1™ compliant. PLUS+1 compliance means our valves are directly compatible with the PLUS+1 machine control architecture. Adding solenoid valves to your application using PLUS+1 GUIDE software is as easy as drag-and-drop. Software development that used to take months can now be done in just a few hours. For more information on PLUS+1 GUIDE, visit www.comatrol.com or http://powersolutions.danfoss.com/Applications/PLUS1Compliance/index.htm. The table below details available GUIDE function blocks for controlling Comatrol solenoid valves.
GUIDE function blocks
Proportional Flow Cartridge Valves
Comatrol proportional flow control valves are 2-way, spool-type valves that are directly operated with a proportional electromagnetic solenoid actuator. By controlling electric current, these valves create an infinitely variable orifice.
1. A constant pressure differential is maintained across the proportional valve (variable orifice), which maintains constant flow regardless of changes in operating pressure or load.
2. A constant pressure differential across the proportional valve limits the flow forces acting on the valve spool. At high flow and pressure, the electromagnetic and spring forces can be insufficient to maintain valve operation without pressure compensation.
Typical circuits use restrictive-type or priority-type pressure compensators with proportional flow control valves to control speed of a hydraulic motor or cylinder.
Proportional flow control valves are available with a variety of flow capabilities (variable orifice sizes). By matching this flow capability to various pressure compensator settings, a wide range of flow vs. current control curves can be attained.
Proportional Pressure Reducing/ Relieving Valves
Proportional pressure reducing/relieving valves are 3-way valves that provide a controlled output pressure as a function of electric current, regardless of system pressure or flow (within the valve’s limits). Direct acting designs are available for low-flow applications.
High flow proportional pressure reducing valve functions can be created by using a proportional valve to pilot a differential sensing valve; see differential sensing valve application notes for more information.
Proportional Pressure Relief Valves
Proportional pressure relief valves are 2- way valves that provide a relief pressure as a function of electric current. Both normally-open (increasing pressure with increasing current), and normally-closed (decreasing pressure with increasing current) are available.
The normally-open proportional relief valve is a direct-acting design for low flow applications. High flow normally-open proportional relief valve functions can be created by using a proportional valve to pilot a differential sensing valve; see differential sensing valve application notes for more information.
Common applications for normally-open proportional relief valves are:
Electro-proportional control of system relief pressure; see differential sensing valve application notes for more information.
Electro-proportional remote pressure compensator control for open circuit piston pumps (for more information refer to BLN-10128 Series 45 Open Circuit Axial Piston Pumps Technical Information).
Normally-closed proportional relief valves are available in direct-acting and pilot-operated designs. A direct-acting, normally-closed proportional relief valve is used for low flow applications. For high flow applications, internally pilot-operated cartridges are available.
Electro-proportional control of system relief pressure or electro-proportional remote pressure compensator control for open circuit piston pumps as above, but where system requirements dictate full pressure with no electrical signal.
- Cooling fan speed control in hydrostatic fan drive systems. (For more information refer to BLN-10080 Fan Drives Systems and Components Technical Information).
All proportional cartridge valves are analog-type valves that control flow or pressure as a function of electric current. For this reason, proportional valves should be driven with a current-controlled device that will maintain constant output regardless of changes in system voltage, line losses, or temperature. Typically available current-controlled valve drivers output a pulse-width-modulated (PWM) square-wave signal. An advantage of a PWM signal is that the dither it provides significantly reduces hysteresis. Comatrol recommends using a 100-200 Hz dither for best performance.
Terms and Definitions
Current is the flow of electricity through a conductor or coil, normally measured in amps (A). Steady-state current flow in an electrical circuit can be calculated by Ohm’s Law, as well as voltage and resistance.
Control Control is a feature of almost all valve drivers. The output of analog proportional valves is a direct function of current. If a valve is controlled with voltage, higher solenoid temperatures, which increase solenoid resistance, will result in lower valve output. To compensate for this, most valve drivers are designed with current feedback circuitry. This means that as solenoid temperature rises or as supply voltage and voltage losses change, the current and corresponding valve output are maintained.
Deadband is the range from zero to the minimum current which causes the valve to respond.
Digital Proportional Valves are extremely fast responding valves that are controlled by a precise on-off signal to produce an average output that is a function of duty cycle.
Dither is a “ripple” signal sent to a solenoid to reduce hysteresis. Dither can be a sine, square, or saw-tooth wave superimposed on a PWM signal or it can be a wave on top of a DC signal.
Duty Cycle is the % of time the valve is on divided by total time.
Hysteresis is the difference in output for a given input, depending on whether the input is increasing or decreasing. It is normally expressed as a % of the maximum rated output. For example, if a 160 l/min [42 US gal/min] proportional flow control valve provides 80 l/min [21 US gal/min] with 1 amp-increasing and 88 l/min [23 US gal/min] at 1 amp-decreasing, the hysteresis is:
Imin is the minimum current required for valve response (see deadband).
Imax is the current required for maximum valve output.
Proportional Valves are analog divices controlled by electric current which may be direct current (DC) or a PWM signal.
PWM is an acronym for Pulse-Width-Modulation. Most valve drivers use a current controlled PWM which produces an average output that is a function of duty cycle in order to reduce valve hysteresis and to allow current control without excessive heat generation. A typical PWM output is a square wave from 80-500 Hz.
Ramping is the application of current to a solenoid with a linear or non-linear ramp, rather than an instantaneous step. Ramping current on and off to a proportional valve provides actuators with soft-starts and soft-stops. Ramps can generally be set or pre-programmed into valve drivers.
Resistance is a component’s opposition to the flow of electrical current, usually measured in ohms (Ω). Resistance depends on the conductivity of the material, as well as size, shape, and temperature. Solenoid resistance can vary greatly with temperature; to compensate for this, current-controlled drivers are generally always used with proportional valves.
Threshold is the minimum current required for valve response; see deadband.
Valve Driver is a generic term for any device that sends a signal to a proportional valve. A valve driver may range from a simple electronic circuit attached to a knob or lever up to a microcontroller with custom software and multiple inputs and outputs.
Voltage is the potential for current to flow in an electric circuit, usually measured in volts (V).
Manual Overide Options