Peristaltic pumps

  1. Wedg1e

    Wedg1e They call me Mr. Bodge-angles

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    While you're on, I wouldn't brag about your TV - trichomoniasis vaginalis as I recall :D

    http://www.nhs.uk/Conditions/Trichomonas_vaginalis/Pages/Introduction.aspx
     
  2. Maker

    Maker nEw mEmBeR

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    Don't ask questions
    Does that stand for vagina dentata?:laughing:
     
  3. sardine

    sardine Member

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    Buckinghamshire
    He said Wankel :laughing:
     
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  4. brewdexta

    brewdexta Forum Supporter

    Messages:
    3,898
    Yorkshire
    While sitting on a train full of adolescents talking twaddle at each other incessantly, some kind of college trip to London, apart for diving for the headphones, I needed something to distract me and my mind wandered back to these pumps.

    I have several uses in the brewery

    1. Pumping liquor (hot water in beer making parlance) from the hot liquor tank to the mash tun though the sparging arm (a rotary sprinkler) to start off the mashing process
    2. Pumping wort from the bottom of the mash tun through the heat exchanger and back through the sparging arm (this is called HERMS Heat Exchanged Recirculating Mash System, this improves wort clarity and extraction/conversion of sugars) The heat exchanger keeps the wort at the desired temp.
    3. Pumping more liquor through the sparging arm to sparge the grain (wash) while simultaneously pumping the wort from the bottom of the mash tun to the copper (boiler) balancing the flow in and out is important here, you want the mash to stay wet at the top so you don't disturb it when sprinkling liquor over it otherwise you wash undesirables into the wort.
    4. Pumping the wort from the copper though a plate heat exchanger into the fermentation vessel, this cools the wort from nearly boiling to below 20c in one pass and achieves a thing called the cold break where undesirables come out of solution and settle out.
    5. Various washing tasks both pre and post brewing
    I can get away with one pump except for task 3 at which point it would be handy if the in/and out flow rates were synchronised. So I thought, why not have two circuits on one pump? So one big deep brake drum that can take two pipes and rotors on the same shaft. I want the outer rotor to be able to be disconnected from the drive if necessary. When engaged the 2 rotors will be synchronised so near identical flow rates.

    So I shall be looking for a brake drum with ideally an internal diameter of around 250mm and probably 50mm deep. Tractor drums come to mind.

    Drive wise, I shall chain or belt drive it from a small motor, potentially a DC motor as the power needed won't be great especially if geared. Also easy to adjust motor speed. Having said that I have a 1/3 HP 3 phase motor and gearbox knocking about, however the DC motor is unlikely to chop your fingers off if you stick them in the pump :)

    The rotors for squeezing the pipe will need some nylon or rubber rollers so I shall keep my eye out for some. I'm thinking of 3 or 4 rollers per rotor. the more rollers per rotor the less flow but also less pulsing. If I make it nice and big then I can add more rotors without diminishing flow rate, or speeding up the ,motor which may wear the hose. I don't need a high flow rate so probably start with 4 rollers and see how it goes. The rollers will need some adjustment mechanism to allow the pipe to be replaced and fine tune how much it squeezes the pipe.

    The missus has some pans with "glass" lids, one of those would be ideal to cover the pump, and replace the knob with the mechanism to engage/disengage the second rotor.

    I shall do some calcs on pipe sizes and flow rates...........
     
  5. I may have a couple of Nuffield 10/60 brake drums in the junk pile that may be suitable for your needs. On the Nuffield the brake drums aren't in the hub but are mounted above the axle under the seat, one on either side.
    I need to root through the junk on the back of the lorry to see if they are still there, or if they got scrapped.
     
  6. Here's an image of one pulled from the web:
    [​IMG]
     
  7. brewdexta

    brewdexta Forum Supporter

    Messages:
    3,898
    Yorkshire
    Interesting, and I'm heading your way in a few weeks for a holiday :)
     
  8. brewdexta

    brewdexta Forum Supporter

    Messages:
    3,898
    Yorkshire
    Doing a quick bit of maths, this is not a robust method, just rule of thumb, it assumes perfect pipe sealing at the squeeze point. I shall calculate minimum power needed later.

    12mm ID silicon tube has an internal cross section of 113mm2
    To pump one CC of liquid then the following length of pipe would need to be squeezed
    1cc = 1000mm3
    1000/113 = 8.84mm

    To get 2 litres per minute then the length of pipe needing to be squeezed is 2000*8.84 = 17684mm per minute.

    If the ID of the drum is 250mm, and the OD of the pipe is 18mm circumference of the centre of the pipe is 232mm*π=728mm however there is an area where the pipes exit the drum, call this 128mm to make a nice round 600mm of available tube to squeeze
    17684/600 = 30 rpm to get 2 litres per minute.

    Evidently you don't want to go too fast with peristaltic pumps as the tube has to recover its previous shape before the next squeeze and you can wear the pipes out quickly. I'm not sure of the max speed, this will depend on the tubing type, wall thickness and temp of the liquid but I think I could probably go to 60rpm so with this drum and pipe size maybe 4 litres a minute. This is fine for most of what I need although I would like a bit more top end to be sure as this is only a rough calc assuming no back-flow.

    Multiple rollers doesn't necessarily increase flow for a given rpm but does lessen the pulsing, I think I will rig up a very basic prototype and have a play with different numbers of rollers, roller diameter, speed etc. and measure flow.

    Yes, I'm on the train again and bored! It may be a while before I rig up the prototype.......
     
  9. pitmole Member

    Messages:
    39
    swuk
    Bit of resurrection here, but just a bit of info to help, I designed a twin peristaltic pump for mixing polyurethane resin for an industrial foam filling and things to consider are, external housing needs to be very rigid as the pressure requirement goes up, shaft bearings need to be seriously well supported to counter the leverage of the rotors, a brake drum with reversed hub is a good place to start from that point of view. Simple nylon castors with roller bearings bolted to a steel rotor with shims in between is a standard industry way of adjusting for pressure and cut off, more rotors don't really improve flow rate once tube is correctly compressed but do smooth out pulses.
    Suction power is directly related to the wall strength of the tubing as that is what draws into the pump, peristaltics are much better at pushing than they are pulling for that reason, and tubing life can be massively extended by submerging the whole lot in a tank of lube that suits the tubing.
     
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