Pinch valves

sorry to re-open a old post. might be a silly question but if you use a pinch valve. do you still need to run the pump in reverse to empty the tank

PS. great to meet you all at the show.

Hi Tim,
It depends on what system you are using,you will need to explain what you have in mind.
nigel.

Hi Nigel,

the tank I'm making is going to be a smaller tank for the air to be pushed into, so hopefully it will fill 100% unlike my other one that would only fill about 60% with the air compressed (hope that makes sense). was going to make the pump run both ways but seeing the photo at the start go me thinking it wasn't needed.

Cheers

Hi Tim,
so I think what you are saying is that you are pumping water into the tank and compressing the air above it,if this is the case I would use a non return valve between the pump and the tank so that the pump can fill the tank but cannot empty it,on the bottom of the tank I would fit a servo controlled valve, to empty the tank the valve is opened and the pressure in the tank forces the water out,SO YES YOU CAN RUN THE PUMP TO FILL ONLY, you need a good pump and nerves of steel to run that sort of pressure,you also need to bear in mind that the deeper you go the less effective this system is,you eventually arrive at a depth where the outside pressure is the same as the pressure in the tank and when you open the valve nothing happens,a good failsafe should stop that from happening (you will lose radio signal long before you arrive at this situation).
Nigel.

Thanks Nigel,

Would you advise to setup the pump to run both way's. I would use a solinoid and run the pump both ways but can only find the ones from china but havn't got the time to order one. at least one thing is the folding dive planes are working a treat :)

Hi Tim,
If you are as I described pressurising the tank I don't see any reason to run the pump both ways.

Hi Tim,

I have used the pressurised tank (PT) system in several subs over a number of years. It is a good system but I always had the pump reversible and I would recommend doing this because:

 - With the  PT system you can lose  a bit of the air bubble for various reasons (excessive angles and dangles, sloshing etc.) When you reverse the gear punp you can pull a bit of a vacuum which helps empty the tank completely. Otherwise your sub may stay sunk!

Somewhere on the Forum is a conversation with Grimreaper (Mark) where he confirms the problem.

I don't actually know whether Sheerline do this although I copied the basic concept for my personal use. I use an electronic switcher using an H bridge (for pump reverse) but I don't see why cams + microswitches can't be used. The mechanical skill required rather defeats me, I confess!

BTW I can see what you are doing with 2 tanks. More complicated than a single baffled tank but may fit in more easily?

(Don't worry about refreshing old threads on the Forum. That is the power of a Forum it moves along with new ideas but you can find common answers.)

Here is another approach to a pinch valve which I am mocking up to try.



The servo 'rolls' a bearing on the silicon tube, tube compressed at servo neutral and uncompresses as  servo moves in either direction.

The bearing is from the read-head pivot arm from an old junked computer hard drive.
(Generally available free from your local computer shop)

However the method, if you are putting a side load on a servo then pay the little extra to get a servo with a ball raced output. Its much kinder to the servo.

Cheers

John

Additions after initial testing.....

The force on the bearing from the pipe is offset from the centreline of the servo arm and therefore causes bending of the plastic servo arm to which the bearing is fastened.
Hence perhaps not a good idea without further development, perhaps a stiffening plate or an aluminium servo arm.

Oh well, into the spares box with it.

John

HI do you use an ESC to control the reversing of the pump to empty the tank?
David

You probably can, and it might be simplest.

I didn't, I used an H bridge switcher which gave full forward or full reverse.

A lot of people use the pinch valve servo as a cam to operate microswitches and it should be possible to get these to switch the pump full forward and reverse. (I suppose you don't really need the proportional control of an ESC.)

David

Hi David
How would you set a H bridge up?

David

As you probably know H bridges are just an all electronic way of controlling motors. say, in forwards and reverse.

You need to give them input signals to control direction and on/off.

The way I did it was through the use of a PIC Microprocessor and this also controlled the servo pinch valve. Probably rather more complicated than it needed to be but I now use the same basic approach for proportional control of piston tanks. (Most of these things are written up on this Forum.)

The simple microswitch approach is quite valid and this thread gives more information:

https://www.theassociationofmodelsubmariners.com/t975-simple-on-off-switcher?highlight=Switcher

David