Piston drive - What is it and why do people like them?

I see some lights say they have pistons. How are these different then a flashlight that clicks on the back?

Instead of a mechanical switch, a piston light has a metal sleeve that actuates an electronic switch in the head. This gives the light a unique UI, feel, and some reliability and safety advantages.

https://www.candlepowerforums.com/threads/85527
:wave: It's all there for the reading, enjoy.

The SureFire 8X, 8AX, 8NX, 10X and perhaps others used a slightly different piston drive approach. The battery itself was the piston, rather than a metal sleeve that holds the batteries. The SureFires hit the market much earlier than the McGizmo products.

I've read this over, but I'm failing to see how it is more reliable if the design is more complex.

Maybe I have to much of the KISS mentality. I'm always willing to learn new stuff though

Oh you're right I am sure that's what he was talking about instead of the McGizmo line and the 7777's adaptation. Oops!

passive101 said:

I've read this over, but I'm failing to see how it is more reliable if the design is more complex.

Maybe I have to much of the KISS mentality. I'm always willing to learn new stuff though

Click to expand...

It's much simplier than it looks. There is no mechanical switch to foul or break for example, eliminating two failure modes. Since the switch is always in contact, there is no spark, so no residue.

A piston won't make the clicky sound. The piston is very smooth. Not sure about reliability. There's a simple o-ring, but I don't trust o-rings to keep dirt or water out unless highly maintained (which I wouldn't do). I would guess o-ring maintenance will be high, when compared to a simple rubber boot switch.

Curious... has anyone had a piston type switch fail? I thought there were some scattered incidents, but it seems to have died down a lot over the past year.

snakyjake said:

A piston won't make the clicky sound. The piston is very smooth. Not sure about reliability. There's a simple o-ring, but I don't trust o-rings to keep dirt or water out unless highly maintained (which I wouldn't do). I would guess o-ring maintenance will be high, when compared to a simple rubber boot switch.

Click to expand...

They don't click per se, but they do make a clacky noise. It is not noiseless if you operate it quickly.

You mention about relying on the o-ring, but what do you think seals the traditional tailcap (containing a clicky) to the body? Yet another o-ring...

If you have no desire to maintain any o-rings, you don't need to waste your money on anything over $5 anyhow, since your neglect will eventually kill it.

snakyjake said:

A piston won't make the clicky sound. The piston is very smooth. Not sure about reliability. There's a simple o-ring, but I don't trust o-rings to keep dirt or water out unless highly maintained (which I wouldn't do). I would guess o-ring maintenance will be high, when compared to a simple rubber boot switch.

Click to expand...

O-rings are in any well made light (clicky, twisty or other-wise), and they all require maintenance to ensure longevity and reliability.

My SF 8NX makes no noise whatsoever, regardless of how fast or slow I press the tailcap button.

The main downside for the SF 8NX design is that the battery stick uses a proprietary configuration, where the negative battery contact is a metal ring at the top of the stick that surrounds the usual positive button contact.

passive101 said:

I've read this over, but I'm failing to see how it is more reliable if the design is more complex.

Maybe I have to much of the KISS mentality. I'm always willing to learn new stuff though

Click to expand...

Disassemble the clicky. Now the piston drive doesn't seem so complicated!

Hi guys,

I coined the name piston drive and I think I'll provide a little background on how it came about.

Surefire came out with a really useful switch that is still in play on some of their lights. It's a tail cap switch that basically initially completes the battery circuit with a resistor in series and then on further depression completes the circuit without that resistor dropping the voltage powered to the head. In effect, you have two levels, first low and then high.

A number of us on CPF proceeded to use this simple and effective means of getting two speeds out of a flashlight. I designed a tail cap switch module I named the McE2S which was adaptable to the SureFire E series LOTC switch and provided for 2 speed activation of some of the SF LED heads as well as most of the E-series compatable heads others were building including the Aleph series of heads Wayne Y and I were involved in.

At some point, I was informed that SureFire has a patent on their 2 level tail switch and it would be wise for me to cease building these. I would state that the mechanics of how my module functioned is significantly different in design and I don't know if it actually infringes on the actual design of SF's switch but certainly the net result is the same and I admit that the idea of using a resistor to accomplish the 2 speeds came from SF.

I figured I needed to move the switch action away from the tail cap to avoid conflict. I also figured that if possible it would be nice to have a two speed light that provided two levels of constant current to the LED and no efficiency loss, as resulting from a resistor in series. I came up with the idea of two contact points in the head that would give you two circuits in play driving the LED. Wayne Y designed a number of converters that functioned with this mechanical design goal. We came to think of these as "x2" converters and they sport an initial contact named the Kilroy spring and then a second contact through a "C" shaped ring that surrounds the perimeter about Kilroy. The design of this battery can and exterior cover involved here reminded me of the piston and sleeve assembly in some of the ICE air cooled engines like the VW and Porsche. The terms piston and sleeve were adapted because you have to name the parts something for sake of identification and piston and sleeve made sense to me. :shrug:

There were and are a number of advantages to this design as well as compromises that would not be considered advantageous to some. The actual contact points where the circuits are activated or deactivated are exposed and easy to view when the head is removed for battery change or simple inspection. There was a reduction in number of components as well as seals in this design compared to a design where you have a battery tube and separate tail cap switch; clickie or LOTC.

Since the inception of the PD lights I designed and offered up, there have been some other manufacturers to use this design in their lights.

I concede that there are other lights including some SF lights that were present before my PD design that activate with the circuit making and breaking forward of the battery and at the head.

In a simple tubular flashlight design, there are only so many reasonable and ultimately self revealing means of activation and switching. It isn't rocket science and the granting of any IP may be more a case who was there first than any real breakthrough in innovation or novel design concepts. From one point of reference, perhaps Mag can be granted the modern flashlight IP and even SF considered a "follower".

To my way of thinking, the PD system was not borrowed from previous art. It came to be in order to accomplish battery connections to the converter located in the head of the light and avoid the tail switch means of activation as well as inefficiencies inherent in accomplishing a low level via resistance in the power line and "choking" or dropping the converter out of regulation.

Justin Case is correct in his comments regarding the SF lights that predated my PD. I was aware of them but they did not figure into my design thoughts what so ever because they involve proprietary batteries which bring both anode and cathode forward to the head as an integral element. In my design, the piston in conjunction with the replaceable and separate battery accomplish the same result but I didn't come about this design thinking in such lines. The Streamlite Strion or at least one I picked up a number of years ago did follow in the same form as these SF lights and if you are inclined to call the SF lights a piston drive then this Strion would be included I would think.

The image below shows a cut away cross section of my PD design which may or may not help shed some light on what at least I consider a Piston drive to consist of:


The light orange represents the "piston" and its contact with the green Kilroy accomplishes low output and then further forward, it contacts the yellow contact ring as well putting you in high or the second mode. I have since the original PD design used the same piston and sleeve for activation of two separate converters with their independent LED arrays which is the basis of my LunaSol design.

Hopefully this post sheds some light on what the Piston drive is about. As to why some people like it, I leave that to others...

Thanks for the history Don!

I love the piston drive because of the versatility of use. I generally hold my lights with the head between my index finger and thumb and so I like twisties. There are times however when I want a quick flash of light so if I hold the light with my thumb on the piston I can push down the piston and get either a momentary low or push further for a momentary high. I can also twist the head for constant on low and push the piston for momentary high. Overall It's just my favourite design.

This is how the converter looks like in such a light:




The first iteration, the legendary McLuxIII-PD:




One very cool aspect is an all-metal tail without a rubber boot:




In bare titanium, you get basically a titanium-only exterior:




This switching method is very intuitive and reliable, it is KISS, either for momentary or for constant activation.

bernie

Oddjob said:

Thanks for the history Don!

Click to expand...

+1, Very illustrative.:thumbsup:

I favor my piston drive lights above all the others in my collection, whether they're my two Nitecore D10's (is 4sevens coming out with one or did you mean the Nitecore lights?) or my two Lunasol 20's. Though they both use piston drives, their UI's are different because they are two differently designed lights. My wife is often asleep when I go in and out of my bedroom and these lights are ideal since they make lots less noise than traditional clickies. I prefer the UI on my LS20's, but the D10's are a VERY close second. Plus, you can't mount a tritium vial into a rubber boot! :candle:

Marduke said:

You mention about relying on the o-ring, but what do you think seals the traditional tailcap (containing a clicky) to the body? Yet another o-ring...

If you have no desire to maintain any o-rings, you don't need to waste your money on anything over $5 anyhow, since your neglect will eventually kill it.

Click to expand...

The difference is that the piston o-ring is constantly being used and seems to require some sort of lubrication. And it seems that when the piston is moving back, there's a lot more opportunity for dirt to get into the cylinder.

Or put another way...put a piston operated light and a traditional clicky in some mud or sandy environment, and start clicking. Which one will fail first? Which one is going to need more maintenance? In my situation, I sometimes have my light in mud, dirt, and sand. I prefer a more "environmentally sealed" switch, which is why I like the rubber boot.

If there's a dent in a piston light, how will it affect the operation of the switch?

snakyjake said:

The difference is that the piston o-ring is constantly being used and seems to require some sort of lubrication. And it seems that when the piston is moving back, there's a lot more opportunity for dirt to get into the cylinder.

Or put another way...put a piston operated light and a traditional clicky in some mud or sandy environment, and start clicking. Which one will fail first? Which one is going to need more maintenance? In my situation, I sometimes have my light in mud, dirt, and sand. I prefer a more "environmentally sealed" switch, which is why I like the rubber boot.

If there's a dent in a piston light, how will it affect the operation of the switch?

Click to expand...

In your situation, I'd think that the sand or dirt will only get into the piston if you activate the light while it's submersed in said substances. Don does NOT describe his lights as dive lights (I think because he doesn't want to be responsible for people who don't maintain o-rings as they should) but he and others consistently take PD lights snorkeling and (please correct me if I'm wrong, Don) diving. If water won't penetrate well-maintained o-ring seals, I fail to see how dirt and sand would, though I've been wrong before!

As for dents in the piston, unless you have the piston disassembled and exposed, I fail to see any way to dent it. The button itself is pretty thick, if you dent that part, you'd dent the aluminum (or titanium!) surrounding it as well. I suppose if you dent the piston (while disassembled), it wouldn't slide as well, but then again, if you disassemble a clicky switch, you could also pierce the rubber boot, break a contact wire on the switch, lose or dent a retaining ring, etc. At least with the piston, there's one piece to keep track of. I've taken apart clicky switches, I'd much rather maintain my piston drives. But to each his own, that's why there are so many options. To the OP, why not invest in a Nitecore? It'll whet (yes, that's the right spelling and word) your appetite for McGizmo lights, so be forewarned! :twothumbs