A door push check combines a spring that closes the door with an air cylinder that slows closing. Hiscox’s example has a piston valve for admitting air readily during opening and an adjustable small outlet for controlled discharge during closing.
Door Push Check Interactive Calculator
Explore a spring-closed door with a pneumatic check. Set the door and frame mounting pins, opening angle and cylinder bore. The plan view calculates pin distances and piston travel; the cutaway shows free air admission on opening and restricted exhaust on closing.
Equation Used
- Fixed frame pin lies perpendicular to and below the closed-door line.
- Door pin remains at the entered radius from the hinge.
- An independent hinge spring closes the door; the air check limits speed.
- Full piston area is used for blind-chamber volume; rod-side volume is not calculated.
- Opening/closing playback timing is illustrative, not a pneumatic simulation.
The calculation is for the stated mounting arrangement, not an exact dimensional copy of the historical device. It predicts travel and displaced chamber volume. It does not calculate closing time, spring torque, latch retention, air flow or a load rating.
A spring closes; an air check resists
The upper plan view shows the door, its hinge, a fixed frame pin and a pin carried by the door. A spring at the hinge represents the separate closing element. As the door opens, the changing pin distance extends the damper.
The lower cutaway expands the pneumatic function. Pulling the piston outward increases the blind chamber volume. A one-way passage through the piston admits air into it. During closing that passage shuts, so the reducing chamber discharges through the restricted base outlet instead.
The cutaway illustrates flow direction and valve state. It is not a manufacturing section of the historical product. Its piston position follows the same normalized travel calculated for the moving door.
Checking the mounting travel
The dimensional calculator helps compare one explicitly defined mounting arrangement. It reports the closed and open pin distances, their difference, and the swept air volume for an entered bore.
These measurements can inform a later component-selection check. They do not identify a suitable commercial closer or establish closing force and speed. The spring supplies closing torque while the air restriction controls resistance during closing.
Distance between the mounting pins
Place the door hinge at H=(0,0). The fixed damper pin is A=(0,−a), and the door pin is B=(r cos θ,r sin θ). The squared distance between them is r²+a²+2ra sin θ.
At a closed door, θ=0 and L_closed=√(r²+a²). At the selected open angle, L_open follows the same distance formula. Required piston travel is L_open−L_closed. Over the allowed angle range this is also the maximum-minus-minimum distance.
The blind chamber swept volume is piston area times travel: V=πD²S/4 in mm³. Dividing by 1,000 gives mL. Bore changes volume but not the geometrically required stroke.
At 90°, dL/dθ=ra cos θ/L is zero. The damper consequently has no instantaneous moment arm about the hinge at that endpoint. The example retains an independent hinge-closing spring.
Comparing mounting dimensions
Start with the default door pin 300 mm from the hinge and frame pin 100 mm below the closed-door line. The closed pin distance is approximately 316.2 mm. Opening the door to 75° increases the pin distance to about 397.4 mm, requiring about 81.2 mm of travel.
A 25 mm bore displaces about 39.9 mL over that stroke. Doubling bore would multiply volume by four while leaving both pin distances unchanged. Increasing the opening angle increases travel until the 90° endpoint.
Travel is not closing performance
A larger piston area moves more air for a given stroke. That alone does not predict resistance or closing time: pressure, leakage, the adjustable restriction and the changing spring torque also matter.
The simulation uses a shorter opening segment and a longer closing segment only to explain the free-inlet and restricted-exhaust states. It does not solve compressible flow. The drawn cylinder and rod proportions are explanatory; the selected device must accommodate the calculated distances and travel.
Door push-check questions
Does the cylinder close the door?
The separate spring supplies the closing action. The pneumatic check resists the closing movement.
Why is opening less restricted?
The piston’s one-way inlet opens to admit air into the expanding chamber.
What changes with bore?
The swept chamber volume changes with bore squared. Mounting distances and required stroke stay the same.
Is the displayed time a prediction?
No. Playback timing illustrates the two valve states and is independent of a real airflow calculation.
What do the calculated outputs describe?
The outputs describe pin distances, required piston travel and swept air volume for the stated mounting arrangement.
Reference
Gardner D. Hiscox, Mechanical Movements, Powers, Devices and Appliances, mechanism 1544, printed page 374 (PDF page 384). The illustration combines the historical spring-and-air-check principle with the assumed door-pin layout described above.
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