P14 Series Pressure Actuated Mechanical Sequencer

Transcription

1 P14 Series Pressure Actuated Mechanical Sequencer Master Catalog 125 Pressure Controls Section P Product Bulletin P14 Issue Date 0996 Application P14 mechanical sequencers have multiple SPDT electric Pennswitches operated in sequence from a single pressure source. Typical applications include: Head pressure control of refrigerant condensers by multiple fan cycling. Refrigeration system control from a refrigerant pressure signal. All Series P14 sequencers are designed for use only as operating controls. Where an operating control failure would result in personal injury and/or loss of property, it is the responsibility of the installer to add devices (safety, limit controls) or systems (alarm, supervisory systems) that protect against, or warn of, control failure. Features Accurate repeat performance. SPDT, totally enclosed snapacting Pennswitches. Single point adjustment moves set point of all stages by the same amount. Calibrated scale reads on set point of stage specified by equipment manufacturer. Pressure ranges for a variety of applications. Models with 3 to 5 stages available. General Description The P14 mechanical sequencer is supplied in open construction (less cover) for panel mounting. Pennswitch terminals are supplied with No. 8 binding head screws. Optional 1/4 in. x in. male quickconnect terminals are available. Fig P14 Mechanical Sequencer. The switch differential and interstage differential are factory set and are not field adjustable. This permits package equipment manufacturers to specify the cycling of their equipment without the possibility of field misadjustment or erratic sequencing. All stages are set to new operating points simultaneously, within the range of the control, by a single range screw Johnson Controls, Inc. 1 Code No. LIT

2 Range and Application Definitions Operating Range The total span in psig over which the control may be operated from the lowest trip point of Stage 1 (lowest) switch to the highest trip point of the highest stage. Scale Range (See Specifications, Table 1.) The span of adjustability of the highest operating point of Stage 1 (lowest) switch. (Lowest operating point of Stage 1 will be below this point by the amount of the Stage 1 differential -- see Range and Differential Specifications. ) Higher numbered stages will operate above this scale setting within the limitations shown in Range and Differential Specifications and A, Figure 2. Uniform Switch Differential (See Differential Specifications in Table 1.) Describes controls which operate every stage at the differentials shown and are nonadjustable either in factory production or in the field. Variable Switch Differential (See Differential Specifications in Table 1.) Describes controls which provide factory set nonuniform stage differentials as shown in the Operating Example, Figure 3, and Customer Requirement Form. (These models are NOT field adjustable.) 2 P14 Product Bulletin

3 Maximum Throttling Range The maximum change in pressure between the pressure decrease trip point of the first stage and the pressure increase trip point of the highest or last stage. (See A, Fig. 2.) Minimum Interstage The smallest allowable change in pressure between similar switch actions of successive stages. (See B, Fig. 2.) Maximum Allowable Pressure The maximum pressure that may be applied to control pressure element at infrequent intervals without damaging the element or seriously changing the setting. Optional Constructions Terminals 1/4 in. x in. male quick connect terminals at extra cost. Connectors Pneumatic control types (4/34 and 7/50 psig [28/234 and 48/345 kpa] range) have 1/8 in female connector. Refrigeration controls have 36 in. capillary with or without 1/4 in. flare nut, as required. Enclosure Only Available for field installation. Miscellaneous Specifications Frame in. (2.36 mm) cold rolled steel. Finish Gray enamel. Contact Units SPDT, totally enclosed snapacting, Pennswitches. Differential The switch differential and interstage differential are factory set and are not field adjustable.! CAUTION: The pressure operating points of all switches must fall within the Minimum Low, Maximum High Switching Pressures, Maximum Throttling Range and Minimum Interstage as shown in Range and Differential Specification, Table 1 and Fig. 2. Selection of differential and interstage settings may limit the total number of stages available within Maximum Throttling Range specification for the range selected. Electrical Ratings Type Number Selection Type Number Number of Stages Type of Differential Electrical Rating at 120 VAC P14JCA 5 Standard, Fixed 16 Amps P14JJA 3 Close, Fixed 6 Amps P14JKA 4 Close, Fixed 6 Amps P14NBA 4 Adjustable (1) 16 Amps (1) Factory set to customer specifications. P14 Product Bulletin 3

4 Shipping Weights (Approx.) Individual Pack 3 through 5 stage models -- 4 lbs. (1.8 kg) Repairs and Replacement Field repairs must not be made. For a replacement sequencer, contact the nearest Johnson Controls wholesaler. Ordering Information To order, specify: 1. Quantity on order. 2. Product Number, if available. 3. If Product Number is not available, specify P14 and: a. Number of stages required. b. Application. c. Range. d. Type of switch differential. 1.) Standard, uniform (fixed). 2.) Close, uniform (fixed). 3.) Variable, factory set. e. Type of connector. 1.) Position of capillary, if model with capillary is required. (See Fig. 4.) 4. Settings, see Customer Requirement Form. Control Requirement -- Sample An air signal from a pneumatic thermostat is available to operate an eight stage P14 to control the loading and unloading of two refrigeration compressors. Compressor #1 starts at 25% capacity when the air signal reaches 8 psi (55 kpa). An additional 25% of the capacity is called for as the pressure reaches 9.5 psi (66 kpa), 11 psi (76 kpa), and at 12.5 psi (86 kpa) the compressor is at full capacity. Compressor #2 starts at 14 psi (97 kpa) and capacity is increased in 25% increments as air pressure increases. As the demand for compressor capacity decreases, the control air pressure decreases. Note that the 25% capacity stage of compressor #2 (controlled by stage #5 of P14) will not turn off until after the control air pressure has reduced the capacity of compressor #1 to 50%. Reference to Figure 3 shows that compressor #2 starts when the system load requires 62.5% of the total capacity but does not turn off until the load decreases to 25% of the system capacity. This intentional overlapping of compressor stages reduces the number of compressor starts and, thus increases the life of the equipment. 4 P14 Product Bulletin

5 Switch and Terminal Identification P14 Product Bulletin 5

6 6 P14 Product Bulletin Performance specifications appearing herein are nominal and are subject to accepted manufacturing tolerances and application variables.

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8 Controls Group 507 E. Michigan Street P.O. Box 423 Milwaukee, WI Printed in U.S.A. 8 P14 Product Bulletin