How to use this calculator
- Enter bore, rod, flow, pressure. The rod diameter is the working dimension — in regen it IS the area.
- Check speed gain vs force. A_bore/A_rod multiplies speed and divides force identically; confirm the approach load stays under P·A_rod.
- Size the cap-end path. Valve and line carry pump flow plus the returned annulus flow — the Q_cap output.
- Plan the switch-out. Kick-down, sequence or directional logic returns full-area force for the working stroke.
How it works
Tie the rod end to the cap end during extend and the cylinder pushes against itself: cap pressure forward, the same pressure backward on the annulus. What survives is the area the rod occupies —
v_regen = Q / A_rod · F_regen = P·A_rod · gain = A_bore/A_rod · Q_cap = Q·gain
Speed multiplies and force divides by the same geometric factor, and the cap-end plumbing carries the combined flow. Plain extend/retract numbers (and stroke times) live in the cylinder speed calculator, force at full area in the cylinder force calculator, and what the pump can actually deliver in the pump flow & HP calculator.
Worked example
Verified against the live calculator
A 50 mm bore / 35 mm rod cylinder on
20 L/min at 100 bar:
gain = 1963/962 = 2.04 · v_regen = 346 mm/s (vs 170) · F_regen = 9.6 kN (vs 19.6) · Q_cap = 40.8 L/min
Twice the speed for half the force — and the cap-end line sees double the pump flow while it lasts. The 35 mm rod on a 50 mm bore is almost exactly the classic 2:1 cylinder, which is why the regen extend pace matches the retract pace within a few percent. When the drill bites or the clamp lands, the circuit kicks down and the full 19.6 kN comes back.
Frequently asked questions
How does a regeneration circuit speed up a cylinder?
By sending rod-end oil back to the cap end during extend instead of to tank. With both ends near the same pressure the net working area is just the rod cross-section, so speed becomes Q/A_rod: a 50 mm bore with a 35 mm rod extends at 346 mm/s on 20 L/min instead of 170 — 2.04× faster.
What force can a cylinder make in regeneration?
P × A_rod — the same factor that multiplied speed divides force. The 50/35 example at 100 bar pushes 9.6 kN in regen versus 19.6 kN in normal extend. That is why regen circuits switch out (kick-down or sequence valve) when the work begins: fast approach in regen, full force after.
What is a 2:1 rod cylinder and why do regen circuits use them?
A cylinder whose rod area is half the bore area (rod ≈ bore/√2). In regeneration that makes extend speed equal retract speed and available force exactly half — predictable, symmetric motion that drill-feed and clamp circuits are designed around.
Why size valves for more than pump flow in a regen circuit?
The cap end receives pump flow PLUS the returned annulus flow — Q × A_bore/A_rod in total. The 20 L/min example pushes 40.8 L/min through the cap-end line and valve. Undersizing that path throttles the speed gain you built the circuit for.
Method & assumptions
- Ideal regeneration: both ends at system pressure, no line or valve losses — real circuits lose some gain to the pressure drop across the regen path.
- Extend-only analysis; retract is the ordinary annulus case and is unaffected by the regen plumbing.
- Load above P·A_rod stalls regen mode — the switch-out valve (kick-down, sequence or directional logic) is part of the design, not an option.
- Rod-seal duty and cap-end component sizing follow the combined flow and full system pressure; check the cylinder maker's regen guidance.