Bench Degree·FLUID POWERchapter

Appendix A: The Bench

The whole volume’s kit in one place. Every experiment in this book is on this list, so you should never have to stop mid-chapter and wait two days for a delivery. Each chapter names what it needs when it needs it and points back here; if you would rather order once and be done, order from this list.

Chapter 1 costs ten dollars, and it delivers the entire thesis of the book. The starter set that covers the first eight chapters is about eighty dollars, and a good deal of it is already in the house.

Nothing here is specified by brand or by part number. Every item is described by function, range or grade, so the list stays orderable from anyone, anywhere, for as long as the book exists. Suppliers change and a printed link dies permanently. A specification does not.

Section 1: The starter set, for Chapters 1 to 8

Starter set total: about $80, or nearer $45 if you already own a caliper, scales and a hose.

Section 2: Added for Chapters 10 to 21

Second set total: about $185, or $120 without the axle stands, the dial indicator and the feeler gauges.

Section 3: The things to get free, and where from

Every one of these is worth more than something bought, and all of them are free for the asking.

Asking is the skill here. Every experiment in Chapters 14, 16, 19 and 20 needs a machine you do not own, and in every case the required item is somebody’s permission rather than somebody’s money. Bring the question and no tools, ask before touching anything, and accept a refusal without argument.

Section 4: The one expensive thing, and whether you need it

An air compressor. A machine of 50 litres (13 gal) with a regulator and gauges costs $200 to $350.

You do not need one for Parts I, II or III, which is Chapters 1 to 8 and the entire physics of the subject. Everything there runs on syringes, a bicycle pump, a garden hose and a bottle jack.

Five experiments want one: the water measurement in Chapter 9, the pump-up and duty-cycle test in Chapter 10, the cylinder force measurement in Chapter 11, the draw-down and stored-energy calculation in Chapter 13, and the leak-rate and regulator tests in Chapter 17.

And all five can be done on somebody else’s compressor in a single afternoon. They are measurements rather than builds: a stopwatch, the tank’s sticker, a gauge and a set of scales. Borrow before buying, and if you do buy, buy for the work you actually have rather than for this book.

Two optional instruments worth naming, because they turn an impression into a number:

An ultrasonic leak detector, about $60, which finds compressed air leaks in seconds where soapy water takes an afternoon. Genuinely useful in any shop with air.

A brake pressure gauge that screws into a bleed nipple, about $40, which turns Chapter 18’s computed 7,750 kPa (1,124 psi) into a measured one. Borrow one from a workshop if you can.

Section 5: What you already own more of than you think

A bicycle pump is a positive displacement pump, and Chapter 6 uses it to prove that a pump makes flow rather than pressure, while Chapter 10 uses it to measure clearance-volume loss with nothing but a tyre and a count of strokes.

A pressure cooker is a relief valve whose setting you can compute from a weight and a hole, and whose pressure override you can watch on the stove.

Your car is a complete hydraulic system with a lever, a pneumatic booster, a tandem master cylinder, four actuators, a proportioning function and an accumulator-based anti-lock unit. Chapter 19 measures four numbers off it and computes the rest.

A garden hose and a tap are a hydraulic power unit, delivering about 133 W of fluid power, and they will demonstrate pressure drop, the orifice square-root law, container compliance and water hammer.

Your own lungs produce about 12 kPa (1.7 psi), which Chapter 5 measures with three metres of clear tube taped to a door frame, and which anchors every pressure in the book to something you generated yourself.

And a grease gun develops 70,000 to 100,000 kPa (10,000 to 14,500 psi), which makes it very probably the highest-pressure device in your building. Chapter 22 says why that matters. Do not experiment with it.

Section 6: The experiments, and where they are

Twenty-two, and the whole list fits on the kit above.

The four in bold are the ones to do if you do only four, and they are named here rather than left to the formatting. The two-syringe press delivers the entire thesis of the book for about ten dollars. One syringe, one thumb, two fluids explains every spongy brake pedal ever felt. Computing your own car’s foot-to-pad ratio tells you a number about a machine you use every day that almost nobody knows about theirs. And the McKibben muscle puts a completely different kind of actuator in your hands, so that you understand what a cylinder’s flat force curve is actually worth.

Notice how many of them cost nothing. Thirty-two of the forty-seven need no purchase at all beyond the starter set, and a good many of those need nothing but a machine that already exists, a stopwatch, and permission to look at it. This is a cheap subject to learn honestly, and the expensive half of it is deliberately left to be read rather than built.

The safety gear, which is not optional

Wear this for the experiments the book says to wear it for. The reasons are on the Before You Start page at the front, and in the chapter that owns each experiment.

Section 7: Kits

A single collection covering the starter set and the McKibben materials, ordered once, is the obvious convenience and it is being worked on. When it exists it will be at benchdegree.com/kit/fluid-power, and that address is deliberately the only place it will be published: suppliers and product listings change, and a link printed in a book cannot be corrected. The specifications in this chapter can be taken to any supplier and will still make sense in twenty years.

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