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Youblob (generated from this blueprint's notebook) · CC0
The Double-Acting Cylinder: Push With the Bore, Pull With the Ring
Bramah's press and the hydraulic jack push one way and let the load fall back. Most machines need power in both directions: a digger's arm, a tractor's lift, a press that must open as well as close. The double-acting cylinder has a port at each end, so oil drives the piston out and oil drives it back.
The rod makes the two directions unequal. Pushing uses the whole bore; pulling uses only the ring round the rod. That one fact decides a cylinder's forces and speeds, hides a pressure trap that can burst a hose, and — with a long stroke — lets the rod buckle long before the oil runs out of pressure.
This rung works all three out and builds a double-acting cylinder from a syringe to measure the difference.
初学者
About 3 hours
说明
1
1
Force, speed, intensification and buckling
Force, speed, intensification and buckling
正在加载 Jupyter 笔记本…
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2
Start from Pascal's principle
Start from Pascal's principle
Every cylinder turns pressure into force by area. The embedded blueprint shows it in its first working form, Bramah's single-acting press.
3
3
Make a syringe double-acting
Make a syringe double-acting
A syringe is single-acting: it has one sealed chamber. Make it double-acting by closing its open end.
Measure the barrel bore and the plunger rod with a caliper. 3D-print an end cap that slides over the barrel's open end, with a central hole for the rod carrying an O-ring in a groove (the gland), and a side port with a hose barb. Seal the cap to the barrel with silicone sealant. Cut the plunger's cross-shaped rod down to a round pushrod: glue a steel dowel pin into it so the O-ring seals on a smooth round rod.
Fill both chambers and two hand syringes with coloured water, bleeding out every bubble. Connect one hand syringe to the tip (cap side) and one to the new side port (rod side).
此步骤所需材料：
注射器套装1 个
钢定位销1 个
O 形圈组合套件1 个
硅胶管1 米
硅酮密封胶1 个
水1 升
食用色素（流动显示用染料）1 个所需工具：
FDM 3D 打印机
PETG线材
6 英寸数显卡尺
热熔胶枪4
4
Measure the two directions
Measure the two directions
From your measured bore $D$ and rod $d$, work out the travel that 2 mL should give each way: $2000 / A_{cap}$ mm going out, $2000 / A_{ann}$ mm coming back (areas in mm²).
Push 2 mL into the cap side, with the rod-side hand syringe free to fill, and measure the rod's travel with the caliper. Then push 2 mL into the rod side and measure the travel back. Repeat three times each way. The return stroke is longer for the same volume — exactly the ratio $A_{cap}/A_{ann}$ in the notebook.
Now hold the rod-side hand syringe's plunger firmly and push gently on the cap side: you feel the rod-side plunger pushed back hard. That is intensification. Do not push hard — a syringe is not rated for it.
所需工具：
6 英寸数显卡尺
直尺
透明安全眼镜5
5
A cylinder that misbehaves
A cylinder that misbehaves
Cylinder faults show up as a handful of symptoms.
Flow
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6
Context and honest limits
Context and honest limits
The double-acting cylinder is not one invention but the working form every hydraulic machine settled on: a honed tube, a piston with seals, a chromed rod through a gland with a wiper, and a port at each end. Its sizes are standardised, so a cylinder of one make fits the mountings of another.
**Honest limits.** A cylinder only turns pressure into force; the valve decides where it goes and the pump how fast. Real cylinders lose a little force to seal friction and need cushions at the ends of stroke, which the notebook leaves out. And hydraulic oil at working pressure can pierce skin from a pinhole leak: never feel for a leak with your hand.
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