Piston tank with pump?

[SWESUB]

Hi,

I saw this interesting dive system, and I know about the "Engel" piston system. But what´s the advantage/disadvantage with this system vs "Engel"?

Best regards!

https://www.youtube.com/watch?v=GAKMX1gBrbo

[subdude]

Different concept completely. That one is just using a cylinder to store the pumped water. Most of those peristaltic pump systems use a bladder to hold the water. It seems more complex.

To me, if I'm moving a piston to store the water, why not drive the piston like Engel does? That pump has to be drawing some serious amps to use the water to push the piston.

But, more than one way to skin the cat. Innovation happens with experimentation.

[scott t]

I think he was testing his rolling pump. Too me it looks like you keep the same volume of water.

To gain something you would need a small piston pushing the larger piston (car).
Maybe push/pull the small piston with air.

[Ralph --- SSBN 598]

Using air instead of a liquid is not a good way to move pistons.

Air compresses then can expand explosively.

Liquids for the most part do not compress and when the container ruptures, the pressure is release immediately and there is not the explosive expansion.
Just some liquid to clean up.

The reason the piston works in our subs is the piston fills with liquid and compresses the air in the much larger wtc.
The air pressure is far less than the pressure in the liquid cylinder.
The liquid has a certain volume and will not expand much from that if the pump is not running.

Air under pressure will expand even if the pump is not running should a leak or rupture occur.

[bob the builder]

A full minute to move 400ml of water?

Yoiks.

[thor]

Jim,

I have a unit I've been playing with for almost 2 yrs. It is a piston system driven by a peristaltic pump similar to the one in the video. It works very well and draws very little amperage. It takes about 28 seconds to move 380 ml of water, but I use a brushless motor which makes all the difference. The pump takes up way less room than those units that use a gear box and threaded rod to drive the piston. I really like it. The reason it is not commercially viable is it takes way too long to get the piston and cylinder machined and get the unit tuned. I would have to charge over $500 for a unit. Won't sell enough to make it worth it, but it works very well.

[scott t]

This sketch is what I am thinking for actuating a piston ballast tank.

[SWESUB]

Matt, exactly what I thought, way less room in the WTC than the "normal" piston-tank.
Is it hard to adjust the boyancy with this technique?

[thor]

Not at all. You can dial your sub in precisely with the pump driven unit. Each turn of the pump inserts a tiny volume of water into/out of the ballast tank which makes precision handling very easy.

Subtech has a unit coming out in the fall that uses the very same system, but is a bladder instead of a piston. Much easier to fabricated and much less time to produce. It has been in testing for 2 years as well. It works equally well and I have not had a single bladder rupture in two years but there is a trick to making that work, and we have been running it a lot to see how many cycles to failure. None so far!

You'll see it shortly when it comes out later this fall. The first unit is a 2.5" WTC.

[Upbubble]

It's the system I used, in the end, for my Trumpeter Astute class conversion. It seemed to use the least space out of the many competing static systems and is very simple: only one 6v peristaltic pump and a tank. No valve needed or tank baffles either for obvious reasons. I prefered the tank to a rubber bag becuase, honestly, I can't bring myself to trust any type of rubber good used over and over. And I've had enough trouble with 'waterproof' switches. Better still, this design doesn't demand any long and rather inconvenient threaded rod moving back and forth in the wtc.

I used one of those neat perspex cylindars apparently https://www.aliexpress.com/item/50mm...819704609.htmlused to cool computers that are available on ebay.

I machined the piston out of delrin and installed a couple of 'o' rings. I fitted a magnet sensor switch at the 'tank empty' end - triggered by a rare earth magnet in the piston part - and an ordinary microswitch at the other. The pump is activated by a servo and switch sytem and the whole lot integrated with a diode circuit I saw on a French sub websitehttp://bateaux.trucs.free.fr/ageneral.html. The failsafe is mounted inline with the servo.

In my sub, the ballast tank is quite small (too small really) relative to the size of boat - I needed to get wires around it and there's a lot of other stuff in the wtc - so the surface trim is a little deep: the deck is dry but the real thing would never be that low unless diving. The rudder comes about 3/8" out of the water. However, she can hover and the fill/empty cycle is only about 25 seconds or so. I'd recommend it personally.