More on Perastaltic pumps

[RonP-UK]

I have had one or two people getting in touch about these pumps and asking questions
about performance etc. No problem here, I will always share information with like minded people but felt I ought to clarify a couple of points.
First---these things can be bloody dangerous if used to pump air, the pressures attained
are not something I would welcome into a model sub hull.
Second---the volume of air (or water) delivered is fairly small, you cant rev these things very high or it will tear up the tube about (100rpm max).
Third---I give it up as a crap idea for the above reasons over 20 years ago.
Having said all that, they do work but I tend to build the larger models so the amount of ballast required would take an age to pump with one of these but used for water on a small model it would be fine I am sure.
One has to ask the question WHY?
If you are building a small boat then get in touch with the hosts of this site, they do everything that you need and-------IT WORKS

[Slats]

I have had one or two people getting in touch about these pumps and asking questions
about performance etc. No problem here, I will always share information with like minded people but felt I ought to clarify a couple of points.
First---these things can be bloody dangerous if used to pump air, the pressures attained
are not something I would welcome into a model sub hull.
Second---the volume of air (or water) delivered is fairly small, you cant rev these things very high or it will tear up the tube about (100rpm max).
Third---I give it up as a crap idea for the above reasons over 20 years ago.
Having said all that, they do work but I tend to build the larger models so the amount of ballast required would take an age to pump with one of these but used for water on a small model it would be fine I am sure.
One has to ask the question WHY?
If you are building a small boat then get in touch with the hosts of this site, they do everything that you need and-------IT WORKS

Well said Ron.
I have had similar enquiries with my various pump set ups (not Perastaltic). I have dumped these not as a failed technology, but for simplicity, reliability, service, longevity, and value for money- you can't go past the Merriman / Caswell sold gas/snort system. As an off the shelf components kit or ready built, you can't buy better.

Best
John

[Subculture]

I think I've mentioned this before, but I'll mention it again. There's a sub modeller here in the UK who built a very nice 205 class from scratch. The ballast system is a hybrid, it uses twin piston tanks (similar in design to your tanks Ron with fixed threaded shafts) with proportional control which are mounted each end of a larger central ballast. These account for about 40% of the ballast volume.

The rest of the tank is a type of snort system, but uses a large scratch built peristaltic pump instead of a diaphragm pump. The boat works very well indeed- moves up and down like an elevator statically owing to the proportional piston tanks.

One might ask why bother to go hybrid? Well the builder wanted to limit the pressure inside the watertight housing.

[Kazzer]

Well said Ron.
I have had similar enquiries with my various pump set ups (not Perastaltic). I have dumped these not as a failed technology, but for simplicity, reliability, service, longevity, and value for money- you can't go past the Merriman / Caswell sold gas/snort system. As an off the shelf components kit or ready built, you can't buy better.

Best
John

I did this test some time ago, after someone selling RCABS gear was making incorrect claims that our pump had insufficient pressure and wasn't suitable for RCABS systems.

As you can see, the pump is pushing up a 25lb bag of lead shot with no problems. Larry Kuntz gave me a test device that measured both pressure and vacuum and I did several tests on our pumps, and published the results in the specs for the pumps.

The video is running in real time, with no editing, so you can see how quickly the pump fills and pressurizes the bladder.

[RonP-UK]

That sounds an interesting approach, a guy called John Robinson built a darnell "U" class some years ago using the same idea (I made the tanks and perastaltic pump for him)
he had to keep internal pressure down due to the lack of free space inside (he filled it up with electronics and batteries) but an easier solution to this is to do as I did with my old "U" boat
I put an adjustable presssure relief valve in the bottom of the bilge (keel)faceing downwards, the relief pressure was set so that only half of the tank capacity was stored inside and 50%
blown out when I dived. This was then replaced when I surfaced through a snorkel with a one way valve to prevent stored air escaping (simples)It has the beneficial side effect of blowing out any water ingress every time I dive and I dont need any other sort of pump. I did have a water pump to move water from bow to stern for trim but abandoned that idea when I linked the tanks to the Salcon so they trim themselves. The boat is self trimming, self baling,self levelling and 30 years old (nothing is new)

[roedj]

... but an easier solution to this is to do as I did with my old "U" boat. I put an adjustable presssure relief valve in the bottom of the bilge (keel)faceing downwards, the relief pressure was set so that only half of the tank capacity was stored inside and 50% blown out when I dived. This was then replaced when I surfaced through a snorkel with a one way valve to prevent stored air escaping (simples)It has the beneficial side effect of blowing out any water ingress every time I dive and I dont need any other sort of pump. I did have a water pump to move water from bow to stern for trim but abandoned that idea when I linked the tanks to the Salcon so they trim themselves. The boat is self trimming, self baling,self levelling and 30 years old (nothing is new)

Ron,

Very clever, that.

I'm wondering though how did you surface if 50% of your air was gone. Did you simply drive the boat to the surface where the snorkel system could replace the missing air?

If you had a fail safe, what did it do?

Thanks for your time,

Dan

[Subculture]

Well you can at least surface to 50% of the scale waterline without pulling a vacuum in the sub, which is quite high on a Type VII.

Old article of Ron's in MMI.

[roedj]

Well you can at least surface to 50% of the scale waterline without pulling a vacuum in the sub, which is quite high on a Type VII.

Subculture,

I realized that about 30 seconds after I sent the question. Every so often I have to remind myself that one does NOT have to blow the entire ballast to surface to where a SNORT like system can function.

Thanks for the article. It's very informative.

Dan

[Subculture]

There were a lot of excellent articles on model submarines written in MMI back in '80's and 90's. Unlike the rival UK publication 'Model Boats' the new kid on the block which arrived about '83/84 published a lot of information about model subs. Unfortunately there is less written now, presumably lacking a regular writer for the old column 'Up Scope'.

Traplet still supply three excellent publications on model submarines, and I assume they must continue to sell well as two of them have reached second editions and all three are still available. It would be nice to see a lot of the early articles collated into a publication of some type. As Ron rightly says, nothing is really new, but folk entering the hobby ask the same questions over and over, partly because there is still very little reference in this hobby, and much of it is still looked on as a black art.

Some things that have changed are the availability of high quality electronics specifically for subs, years ago, much of this had to be home made or the devices were quite large or difficult to source- the introduction of the microcontroller is a big factor here.

Also we now have miniature air pumps available cheaply, and the exponential improvement in batteries has improved things especially for those wishing to model smaller boats.

[RonP-UK]

Good grief---I,ve got hair in that picture