Push-Pull Solenoids

1. Design and Features
The push-pull solenoid design utilizes a coil with the maximum amount of magnet wire in the smallest amount of space. This coil assembly is then packaged in a metal housing using highly permeable steel thus obtaining maximum force and minimum size and weight. The armature design utilizes a secondary magnetic circuit, which provides an increased output of force of 20-50% (comparison is made of a 491C with a stroke of 3 mm). The push design is meant for applications that require relatively short strokes (0-8mm). In general, the solenoid height is half the outside diameter. The output shaft is attached to the armature and can be attached to either end of the solenoid. Thus, attaching to the shaft on the base side actuates as a push solenoid. Attaching to the shaft on the armature side actuates the solenoid in the pull mode.

2. Stroke and Force
The push-pull solenoid is available with 2 standard pole piece configurations. The conical pole is meant for medium strokes (3-8mm). The flat pole piece is designed for short strokes (0-3mm), and where high holding force is required. Force-stroke curves for each size and configuration are shown in the catalog. For the best performance and efficiency, the stroke should be kept to a minimum.

3. Operational Considerations
A) Temperature
The coil data of push-pull solenoids shows the values at ambient temperature 20°C and with a standard heat sink. If a solenoid is used at a rating shown in the coil data, it is designed so that the coil temperature rises and reaches equilibrium at approximately 85°C. In applications where the ambient temperature is higher than 20°C or the heat sink is smaller than indicated in the catalog, possible thermal damage can occur. Temperature rise tests should be performed by the customer to assure that the coil does not reach 120°C. Coils can be constructed to operate at temperatures higher than 120°C without thermal damage. Please consult the factory for details.
B) Air Gap Spacer
The push-pull solenoid uses an air gap spacer between the armature and the case. This spacer is installed to prevent the armature and base from coming into mechanical contact with each other, which would cause residual magnetism.
C) Return Spring
The push-pull solenoid does not include a return spring. Therefore, the application must include a return spring.
D) Shaft Modification
It is not recommended that the customer modify the shaft, as the shafts are fabricated before assembly. Any special configuration can be supplied. Please consult the factory for details.
E) Installation of Solenoid
The size 191C and 191F use tapped holes for mounting in the base. Caution needs to be observed that the mounting screws used to attach these solenoids are the correct length so as not to damage the coil.

4. General Characteristics
Insulation class : Class E (120°C), Lead wire class A 105°C
Dielectric strength: AC 1000V 50/60 Hz 1 min. (at normal temperature and normal humidity)
Insulation resistance: More than 100 Megohm at DC 500V megger (At normal temperature and normal humidity)
Expected life: Standard life: 2 million cycles,  Extended: 10 million cycles, (Solenoid cycle life is very dependent upon side load, frequency of use, and environmental conditions. Cycle life tests should be performed by the customer.)

5. How to Select a Solenoid
Before selecting a push-pull solenoid, the following information must be determined:
A) Force
The actual force required in the application should be increased using a safety factor multiplier of 1.5 to arrive at the force value that should be used in your specification.
B) Duty Cycle
Use the aforementioned formula to calculate duty cycle. Also note the maximum on time.
C) Stroke
Stroke is determined by application requirements.
D) Operating Voltage
Operating DC voltage is determined by the application and voltage available.

After determining these specifications, one can find the correct size solenoid for the application, using the force-stroke characteristic tables and graphs. The coil data is also shown for different sizes of magnet wire. If the exact operating voltage is not in the coil data table, use the nearest voltage shown in the table. When the operating voltage falls between 2 coil sizes, always use the higher AWG numbered coil to prevent potential thermal damage. To determine the force output of the solenoid after temperature rise, please use the amp-turn force graphs after calculating the amp-turns.