Electric Pressure Regulating Valves
CDS Series
The Sporlan CDS family represents a line of electronically controlled step motor valves, designed to contribute minimal pressure drop to the system. In addition to their traditional application as Electric Evaporator Pressure Regulators, CDS valves can also be applied as Heat Reclaim, Head Pressure Control or Liquid Line Differential valves. By providing synchronized signals to the step motor, discrete angular movements are translated through a Digital Linear Actuator (DLA) into precise linear positioning of the valve piston. The balanced pistons and ports are uniquely characterized, providing superb flow resolution and performance across a range of applications and operating conditions. The CDS valves interface easily with microprocessor based controllers, including Sporlan supplied controllers.
- Step motor operated for precise control
- High resolution drive assembly
- Solenoid tight seating
- Corrosion resistant materials used throughout
- Field proven reliability
- Low power consumption (4 watts or less)
- Balanced port designs
- Compatible with most HCFC and HFC refrigerants and oils, in addition to subcritical CO2
- Self lubricating materials used for long life
- High linear force output
THE VALVES
Sporlan CDS valves are available in two styles - the CDS-2, CDS-4 and CDS-7 provide 2500 steps of resolution, while the larger CDS-9, CDS-16 and CDS-17 provide 6386 steps of resolution. 12 VDC step motors coupled to an integral gear reduction system give the valves unparalleled accuracy and repeatability over the entire operating range. Capable of tremendous versatility, CDS valves can be used to replace a variety of mechanical and solenoid valves throughout typical refrigeration and air conditioning systems, where low pressure drop and precise refrigerant flow control are desired. And because the valves are powered by an external controller, no pilot lines or high to low side bleeds are required. The tables found at the back of this bulletin show actual capacity at specific conditions representative of several typical applications.
CDS valves have years of proven field performance, but also offer excellent serviceability. A simple cartridge design permits all moving parts to be replaced as a unit, leaving the valve body in the line. The CDS-2, CDS-4 and CDS-7 also offer a removable cable, which reduces damage potential during brazing, and eliminates rewiring when servicing the motor cartridge. Caution: The CDS-9, CDS-16 and CDS-17 feature a hermetic cable, and no attempt should be made to remove the cable.
VALVE OPERATION
The CDS valves are driven by the electronically controlled rotation of a step motor. The step motor drives a gear train and lead screw to position a piston, modulating flow through the port. The two-phase motor is driven in bipolar mode. Two discrete sets of motor windings are powered in sequence to rotate the rotor 3.6 degrees per step. Polarity of the drive signal reverses for each step. The sequencing is accomplished electronically through a bipolar drive circuit, an example of which is shown in Figure 1. Further exploration of this drive circuit and alternatives is beyond the scope of this bulletin.
CDS-2, -4 and -7 valves have 2500 steps and CDS-9, -16 and -17 have 6386 steps. See specifications for valve stroke and resolution. Although phase resistance for the CDS-2, -4 and -7 are different (100 ohms) from the larger valves (75 ohms), no controller modification should be necessary.
The CDS-9, -16 and -17 are supplied with a hermetic cable connection. CAUTION: No attempt should be made to remove the hermetic cable. The CDS-2, -4 and -7 are supplied with a removable cable. All external parts of the valve are brass, copper or stainless steel, and meet or exceed ASTM standard B-117 for corrosion resistance.
Although 20 feet is the standard cable length, the leads can be supplied from 10 feet (3 meters) up to 40 feet (12 meters) to suit specific customer requirements. If a valve must be installed more than 40 feet from the controller, a short lead wire must be used with an extension of heavier (14-gauge) wire, due to voltage drop considerations. Unless otherwise specified, the terminal end of the wires will be supplied stripped and tinned.
Total power consumption is less than 4 watts when operating a rate of 200 steps per second with standard L/R drive circuitry. Faster step rates up to 400 steps per second may be obtained with properly configured current limited chopper drives. Refer to the motor specifications or contact Sporlan for more information.
The small CDS valves have a maximum rated pressure of 700 PSIG (48 bar), while the larger valves have an MRP of 680 PSIG (47 bar). Allowable ambient temperatures are -50°F to 140°F (-45°C to 60°C), while fluid temperatures up to 240°F (115°C) are acceptable.
APPLICATION
The CDS valves are designed for precise and energy efficient control of evaporator temperatures, in addition to modulating temperature control of reclaim condensers, head pressure or liquid line differential control, and other applications where low pressure drop contribution is desirable. Modulation around a set point is obtained by regulating refrigerant flow in response to signals generated by an electronic controller and sensor combination.
Sporlan is not responsible for system design, for any damage arising from faulty system design, or for misapplication of its products. If these valves are applied in any manner other than as described in this bulletin, the Sporlan warranty is void. Please contact your Sporlan Sales Engineer for assistance with your specific application.
It is the responsibility of the controller manufacturer to provide suitable drive circuitry and power supply. Sporlan will assist where necessary, but accepts no liability for improper control of the valve. Careful consideration should be given to the interaction between the valve controller and system controller (if independent), to ensure proper behavior in all system conditions. Control strategy is a critical factor in determining valve duty cycle and control capability.
It is strongly suggested that power to the valve be disabled when not actively stepping. It is recommended to apply power for 25 ms prior and subsequent to stepping, and to pause 25 ms before reversing direction.
Conventional initialization routines, which include overdriving the motor closed to ascertain the zero step position, are acceptable. Overdriving open is not recommended. When properly controlled, Sporlan CDS valves should not lose steps, and therefore it is not recommended to perform a full initialization every time the valve is closed. It is however reasonable to overdrive a small number of steps to ensure full closure every time the valve is closed, or to perform an initialization at a regular interval when convenient (e.g. during system defrost).
SELECTION EXAMPLE – SUCTION (TONS)
Refrigerant: R-404A
Liquid Temperature: 80°F
Evaporator Temperature: 20°F
Evaporator Capacity: 4 Tons
To select a valve for these system conditions, look at the suction capacity tables, and locate the set of columns applicable to R-404A. To apply a valve with minimal pressure drop, the 0.5 PSI column should be used. Adjust for the liquid temperature by multiplying the appropriate correction factor (shown at the bottom of the page) to each capacity value. For an evaporator capacity of 4 tons at 20°F, a CDS-16 with a capacity of 5.93 * 0.87 = 5.16 tons would be required. Note that this valve is available in angle configuration only, therefore a straight through CDS-17 (with a capacity of 6.2 * 0.87 = 5.39 tons) could also be selected. A more economical approach would be to select a CDS-9 at 1 PSI drop, which has a capacity of 4.82 * 0.87 = 4.19 tons. To extend the example, if a 3 PSI drop could be tolerated, the best cost solution would be to select a CDS-7 with a capacity of 5.38 * 0.87 = 4.68 tons.
