A double-acting lift-and-force pump fills one cylinder end while discharging from the other. Four check valves switch the flow paths automatically as the piston changes direction. This vertical reconstruction follows Hiscox’s mechanism 511, with suction on the right and delivery on the left.
Double-acting Lift and Force Pump Interactive Calculator
Explore the vertical four-valve pump shown as Hiscox 511. The right-hand suction passage feeds alternate cylinder ends; the left-hand delivery passage collects the output. Enter the upper rod diameter to compare the two stroke volumes accurately.
Equation Used
- Incompressible fluid and ideal check valves without leakage.
- The piston rod occupies the upper chamber only.
- A complete cycle consists of one downstroke and one upstroke.
- Rod diameter satisfies 0≤d<D; zero represents neglecting rod area.
- The piston reverses smoothly; instantaneous displacement rate is zero at reversal.
The former 2AS result is the rod-area-neglected limit. A nonzero upper rod makes the upper-end delivery smaller. Invalid rod/bore combinations are shown without substituting a different rod diameter.
Trace suction A and delivery B
The common suction passage A runs up the right side of the cylinder. It branches into the upper and lower working spaces through separate inlet checks. Delivery passage B runs up the left side and receives liquid through two separate outlet checks.
On the downstroke, the upper space grows and takes liquid through its right-hand inlet. The shrinking lower space discharges through its left-hand outlet. On the upstroke, the lower inlet and upper outlet open instead.
The upper rod stays connected to the piston and passes through the top cover. It occupies part of the upper working area. The valve and fluid-arrow sequence follows the motion of that piston rather than an unrelated decorative cycle.
Use dimensions to compare delivered volumes
Bore determines full piston area, stroke determines travel, and rod diameter corrects the upper chamber’s swept area. The calculator reports the volume from each end and their sum over a complete down-and-up cycle.
This is a geometric displacement calculation. It does not determine a safe suction height, delivery pressure, required motor size or a pump’s ability to handle a particular liquid. Those depend on installation conditions and the actual machine.
Include the upper rod
For bore D, rod diameter d and stroke S, the full area is A=πD²/4 and rod area is a=πd²/4. The lower end delivers AS on the downstroke. The upper end delivers (A−a)S on the upstroke. Adding them gives (2A−a)S.
When millimetres are used, divide the result by 1,000,000 for litres. The full piston area in cm² is A/100.
The original approximation 2AS is recovered when rod area is neglected. It should not be described as exactly twice the full-area delivery when a finite rod is present.
200 mm bore with a 40 mm rod
For a 600 mm stroke, the lower end delivers approximately 18.85 L and the upper end 18.10 L. The complete cycle delivers approximately 36.95 L in the ideal model.
Setting the rod diameter to zero gives the rod-area-neglected result of 37.70 L per cycle. Increasing rod diameter reduces upper-end delivery while leaving the lower-end volume unchanged. Doubling stroke doubles both volumes.
Alternating delivery is not uniform flow
The pump delivers during both moving halves of a cycle, but the piston still stops at each reversal. The animation seats all checks at that ideal instant and removes flow arrows. It does not assert constant outlet flow.
The check elements are shown as ideal translating discs so the open and closed routes are easy to follow. Their exact lift, seating dynamics and pressure drops are not calculated. Dimensions shown in the diagram are the entered working dimensions, not dimensions for manufacturing the illustrated casing.
Lift-and-force pump questions
Which passage is suction?
A, on the right. B, on the left, is delivery.
Why does the upper end deliver less?
The rod occupies some of its swept volume.
Why can I select a zero rod diameter?
It reproduces the common rod-area-neglected approximation. The dashed drive line is an idealized connection.
Does the illustration predict maximum lifting height?
No. It shows valve action and displaced volume, not suction pressure or cavitation.
Are two moving halves one cycle?
Yes. Complete-cycle delivery includes one downstroke and one upstroke.
Reference
Hiscox, Mechanical Movements, Powers, Devices and Appliances, mechanism 511, printed page 140 (PDF page 150): vertical double-acting lift-and-force pump with suction passage A and delivery B.
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