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Old 13th Nov 2018, 1:41 pm   #41
Graham G3ZVT
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Default Re: Electronics versus plumbing?

Angus,
What about the Farranti effect?
That always seemed contra-intuitive to me. Can you come up with a plumbing analogy that makes more sense?
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Old 13th Nov 2018, 2:28 pm   #42
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Default Re: Electronics versus plumbing?

Speaking from experience in teaching basic electrics / electronics, on occasions I have found it necessary to resort to teaching some basic mathematics first. Examples: Pythagoras theorem, basic trig., simple equations, etc. - and even the manipulations of fractions. Fortunately, for most of us who are adept with electrical / electronic fundamentals, that knowledge is second nature. For myself, I 'do' maths. for fun - so I find teaching both parts to be enjoyable too.

Al.
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Old 13th Nov 2018, 8:54 pm   #43
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Default Re: Electronics versus plumbing?

Quote:
Originally Posted by Steve_Bell View Post
A basic observation: there is no return circuit needed in plumbing (e.g. neutral wire)...
Sometimes we use the earth as a return, other times we use the sewer. In general hydraulics where fluid tension is used to transfer power, however, the return circuit is usually taken more seriously.

On the other hand, while this is fun, I wouldn't confuse a novice with water analogies unless really needed to get the point across.
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Old 14th Nov 2018, 5:16 am   #44
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Default Re: Electronics versus plumbing?

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Originally Posted by rambo1152 View Post
Angus,
What about the Farranti effect?
That always seemed contra-intuitive to me. Can you come up with a plumbing analogy that makes more sense?
I'm sure the same effect occurs in fluidic transmission lines. The thing to understand about inductors/inductance and capacitors (or fluid inertia and compliance of fluid carrying devices) is that they store energy.

So just as a capacitor can store energy in its electric field and an inductor store energy in its magnetic field, likewise moving fluid has kinetic energy and the stretched wall of a pipe or compliant chamber has elastic potential energy like a spring.

In dynamic situations the stored energy is released, for example an inductor can give its stored energy to a capacitor and the effect is the voltage on the capacitor's terminal climbs.

If you have a moving column of fluid in a tube and you stop it abruptly, there will be a pressure peak, much like any force peak when you try to stop a moving mass.

Depending on the scenario, there can be voltage peaks in electrical systems and pressure peaks in fluidic systems that exceed the value of the average driving pressure or voltage. It is simply due to the nature of stored and released energy from reactive elements, like L and C in electrical systems, or fluid inertia and compliance of fluid carrying objects or fluid filled chambers in fluidic systems.
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Old 14th Nov 2018, 8:39 am   #45
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Default Re: Electronics versus plumbing?

Hydraulic pump is akin to a transformer or balun etc. Passage of energy, not fluid.

As for no return wire needed...surely there is. If theres no circuit theres no flow. If fluid merely oscillates with no flow we have a standing wave analogy

D
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Old 14th Nov 2018, 11:51 am   #46
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I'd disagree - the hydraulic ram pump is akin to a switch-mode converter (boost converter in particular). The long input pipe is the input inductor, the clack valve the switching device, the one-way output valve the output diode, and the air chamber the output capacitor.

Basically as Argus says, and Radio Wrangler in post #12.
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Old 14th Nov 2018, 5:34 pm   #47
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Default Re: Electronics versus plumbing?

It's also quite inefficient in the sense that a lot of water runs to waste (well on down the stream anyway) when it's operating.
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Old 14th Nov 2018, 6:09 pm   #48
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Default Re: Electronics versus plumbing?

Just thought of another one. Thermistor; thermostatic radiator valve. Inspired while watching a heating engineer installing a new combi-boiler at the work premises today.
Alan.
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Old 14th Nov 2018, 6:22 pm   #49
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It's also quite inefficient in the sense that a lot of water runs to waste (well on down the stream anyway) when it's operating.
A hydraulic ram pump - in terms of water, yes. But not quite so in terms of energy. While a lot of the water runs downstream, it's low-energy water, flowing slowly. As the flow builds up, the clack valve operates.

And a switchmode boost converter does this too. A lot of the time, the switching device is closed, and the current from the input circulates back to source through the inductor. When the switch opens, the flow is diverted to the output - just like the ram pump.
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Old 14th Nov 2018, 6:31 pm   #50
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Default Re: Electronics versus plumbing?

While I can accept that a servo-actuator-controlled valve is rather like a thermionic valve/transistor in its 'amplifying' capability, is there a hydraulic equivalent of a Thyratron/Thyristor??
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Old 14th Nov 2018, 7:14 pm   #51
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There are hydraulic valves which do this, yes. Basically a flap held closed against an orifice by a weak spring, such that water pressure acts to reinforce the spring's force - but once flow has started, the pressure across the valve vanishes and the flow itself overcomes the spring's force so that flow continues until it drops so low that the spring can re-close the valve.

Some types of flush toilet cistern use such a valve. Other types work by a siphon (and now I'm trying to think of the electrical analogue for that!)
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Old 14th Nov 2018, 8:54 pm   #52
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An old lady I used to know (long deceased) had a ram pump. There was a pickup tank, which fed the main "room" about 25' away through a 3" pipe. The head was maybe 6' at the most. That fed water to her wooden bungalow 90' higher up. Inefficient in pure terms, but I don't think she would have been happy carrying multiple buckets of water around a quarter of a mile each day. There were about 6 more such pumps in the immediate area. Some pump the (clean) water directly, others use dirty stream water to raise clean spring water to the required destination. A darning needle is the most useful tool for trouble shooting and repair.
Les.
Edit. The pumps I knew had no springs, but an inverted mushroom valve. Falling open under gravity, header water increasing velocity until it raises and slams closed the mushroom. This creates the pressure pulse sending up the water, but also stopping the flow in the header pipe. The cycle repreats continuously.
Les.

Last edited by MotorBikeLes; 14th Nov 2018 at 9:03 pm. Reason: Additional explanation 2nd edit, sp.
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Old 14th Nov 2018, 10:34 pm   #53
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Using water flow as an analogy for electrical theory is not a recent phenomenon. Many of the great inventors known to us all, back in the 18th & 19th century, used these methods.
When I commenced RAF radio training back in 1961, it was used by our instructors. Then 9 years later when I commenced instructor training myself, we were encouraged to do so. In fact, radar mechanics & fitters were sometimes referred to, in RAF slang, as "Plumbers". Most likely because of their use of copper sheathed co-ax, and various metal waveguides.
In civilian life, having built my own house & wired & plumbed it, I was later asked to install 10 en-suite bathrooms in a refurbished highland hotel(owned by an ex RAF electrician). All still working fully after nearly 40 years.

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Old 14th Nov 2018, 10:40 pm   #54
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A friend has a disused ram pump, which is why I know about them. It used river water flow to power the pumping of clean spring water. The maker's plate says "Blake's Hydram" Very big, very heavy and currently set in concrete submerged in water. Available, I think, if anybody wants it. I'm contemplating restoring the water wheel in whose pit it sits.

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Old 14th Nov 2018, 11:56 pm   #55
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Default Re: Electronics versus plumbing?

My error...I didnt mean hydraulic pump, I meant hydraulic motor, as in a power transfer unit. We use them in all the hydraulics in aiir craft. It transfers power and pressure but not fluid. I envisage a transformer, two coils of wire but not connected.

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Old 15th Nov 2018, 12:11 am   #56
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This thread reminds me of how often I used to use electrical circuit analogies in the analysis of simple vibration and noise problems. It was a very common technique through to the 90s, displaced a bit when FEA became cheap enough (in terms of the software, and hardware to run it) that the lumped-parameter assumptions of the circuit analogues could be tested and the frequency range of models extended. Still, where a system lends itself to it and one has an analytical expression for (say) the input impedance to a section with wave-type (distributed) behaviour, one can bolt together lumped- and wave- models and get good results. I really liked the technique, and carried on with it to the point that I was probably regarded as a dinosaur! Great for teaching, too. Beranek's 'Acoustics' is probably the classic reference text, though there were many others.

(Oh - and mention of SPICE made me smile, as I remember folks getting frustrated at the frequency-dependent resistance needed to model the real part of the air load on a loudspeaker, and how that didn't fit very nicely into circuit modelling tools of the time!)
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Old 15th Nov 2018, 8:35 am   #57
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Default Re: Electronics versus plumbing?

Maybe we shouldn't go too deep.

Water flow and pressure works as an analogy for some aspects of electricity and can aid teaching, but expectations that the analogy should fit all aspects will fail because then electricity and water would have to be the same thing.

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Old 15th Nov 2018, 8:42 am   #58
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Default Re: Electronics versus plumbing?

That is exactly right and even the models we have for what we think are electrons or water molecules are only that, models, so as to help us conceptualize the physical events we observe and help fit the experimental findings and again aid teaching.
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Old 15th Nov 2018, 11:22 am   #59
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Default Re: Electronics versus plumbing?

On the other boot, I wonder if the plumbing trade use electricity as an analogy to teaching plumbing to newbies

Lawrence.
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Old 15th Nov 2018, 6:10 pm   #60
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Quote:
Originally Posted by G4YVM David View Post
My error...I didnt mean hydraulic pump, I meant hydraulic motor, as in a power transfer unit. We use them in all the hydraulics in aiir craft. It transfers power and pressure but not fluid. I envisage a transformer, two coils of wire but not connected.
That could conceivably be a transformer-equivalent then.

One hydraulic circuit with a vane motor, another with a vane pump, the two linked by a shaft - yes!

If the secondary circuit is blanked off, then pressure will be there, proportional to pressure in the primary circuit, but there'll be no flow.

Allow a bit of water to flow in the secondary and the 'pump' vane will slowly turn, which grabs motion from the primary motor, which then sucks some water flow. Just like a transformer.

Except that this seems to work with steady flows, whereas a transformer needs alternations. Suddenly I'm jealous of the plumbers...
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