Peristaltic pupmps are basically the type of pumps used in some model sub dive systems- they are also used in the medical industry...,
in laymans terms...( sorry if you understand this but for those who dont.....)
the pump is an electric motor ( about a 540 size in norbert bruggen sub kits) that is geared -the geared output moves a rotating arm, this rototating arm acts as the impellor - as the rotor rotates it depresses a silicone hose squeezing the contents of the hose in one direction or the other, once the motor stops the fluid being pumped cannot move in either direction as the hose remains depressed
( these pumps are the type seen rotating on kidney dialysis type machines...)
the benefit for subs are - they are totally controllable, if you wish to operate the pump for a very short period of time then you can - they are very very controllable if you wish to pump 2ml of ballast water you can !- its not an all or nothing operation !
the other benefit is once the pump is stopped then there is no current draw and also due to the build of the pump no matter what the pressure the water will not and cannot bleed from one side of the pump to the other until the pump is operated, so the fluid pumped stays where you want it !
the pumps are used in the flexi bag system....or as norbert bruggen calls it the gummi sac system-
the basics for model subs ....
you place the pump inside the watertight section of the sub, one end of the tubing is connected to the external body of the sub ( ie out into the water/ flooded area) the other end of the tubing from the pump is connected to a flexible rubber type bag which is also inside the watertight section of the model,
when you launch the model the flexible bag is empty - the model can be sailed on the surface, when you wish to dive you operate the pump, the water is pumped from the wet area/ lake, into the rubber bag inside the watertight chamber, the rubber bag swells due to the water inside, this compresses the remaining air inside the watertight section of the sub..... the additional weight of this water ballast causes the sub to dive / submerge, - to surface the pump is operated in the reverse manner and the water held in the rubber bag is pumped back out into the lake, the bag returns to its normal shape, the air in the watertight section is no longer compressed and without the weight of the water the model is bouyant and the sub will surface...
the advantages of this system is if you operate the pump in short bursts the water being pumped on board is very finely controllable, you can litterally get a sub to 'hang' in the water, neither rising or falling but sitting stationary at a midway between surface and 'sea bed'... the sub has neither negative nor positive bouyancy.
you can also dive and surface at a very very slow speed, which in many models is more realistic......
advantages are,
very controllable dives.
slow speed movements
no leak back with the pump
good if space is tight of you have an unusual space for your dive system ( the flexi bag can be any shape you want so long as it holds the required amount of water ballast required to dive,, and its a compact system compared to some piston tanks containing the same volume of ballast)
disadvantages are
not great for huge subs where large amounts of ballast is required to dive -dives take to long
most of the pumps are designed for 12 volts or higher so if you run a 6volt set up in your sub then you either need a secondary battery to run the pump at the recommended voltage or you run the pump at half speed on 6 volts !
there are several makers of pump - and you can see by the link given above even RS sell such types of pump, but the small one as distributed with Norbert bruggen kits is my favourite ( plus norbert has been doing subs for years, he is the man to know a good pump !)
also carefully investigate the pumps the flow rates and finally the cost before buying, the pumps on RS website are into 3 figures !!!!!! Norbert will sell you one for alot less, and if you speak to the UK Manufacturers office then they are cheaper still !
