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Valving

Peristaltic Valve - gen1

Details
Parent Category: Hydration and Hydroponics Projects
Category: Valving

In my seemingly-endless tinkering with Peristaltic pumps, it occurred to me that the same concept used in a peristaltic pump to move fluid, could also be used to create a valve mechanism. So I decided to give it a shot, and it actually works pretty well!

Design

There are three main elements to the design:

  • The Shoes - These are shown in orange in the above images. These parts include the guides for the tubing, and the wall that the tube will be compressed against when closed. There is one shoe for each tube/channel that is being valved.
  • The Stator(s) - Shown in electric blue in the images. These two parts bolt together, clamshell style, and act as the frame. They also house the main bearing journals that support the rotor.
  • The Rotor(s) - Red and grey in the images. Both ends of the rotor have a motor coupler bearing journal. The rotors also have the attachment points for the bearings that will compress the tubing.

BOM

  • Printed Parts
    • (Qty 2) Frame.stl - These make the Stator
    • (Qty 1) Rotor_Upper.stl
    • (Qty 1) Rotor_Lower.stl
    • (Qty 4) Shoe.stl
    • (Qty 3) BearingCap.stl - These extend the contact patch for the bearing to cover the full tube and also can be easily swapped to vary the compression gap for different tubing and/or seal.
    • (Qty 1) HandCrank.stl - To manually operate the valve - There are also mount locations on the Frame parts to attach a servo, but currently the drive torque required seems prohibitive (in my opinion)
  • COTS

Heat set locations

One of the frames will have four, M3 heat sets inserted for attaching the frames together. These should be inserted from the inside (the smaller diameter).

Both frames will get four, M3 heat sets inserted around the perimeter, for attaching the shoes.

If you are going to insert the M4s into the frames, be careful when inserting the M3s to not obstruct the one M4 hole that intersects. You may want to use a shorter M3 for these holes.

The final M3s go into the Rotor_Upper. I was wanting to test using the expansion of the post when inserting the heat set to make an interference fit with the bearing, but I was too conservative on my post diameter. So no need to have the bearings in place when inserting the heat sets.

 

Four Channel DrumCam Valve

Details
Parent Category: Hydration and Hydroponics Projects
Category: Valving

 

This design is for a digitally-controlled, four ‘channel’ valve assembly. I designed this specifically for the application shown in the picture above, where I wanted to be able to controllably dose from individual reservoirs to individual target plants. By combining a couple of these valves with a peristaltic pump, I could supply four plants from up to three reservoirs.

The valve works by the camshaft pushing steel balls against the tubing passing through the valve. The channels are closed except when the cam rotates such that the ‘pocket’ for that channel is rotated such that the ball can lift and release the tube. The video below shows one in action.

Find it on Printables

Design Overview

drumcam_4ch_xsec_4a05b.png

A good friend (and far better engineer than I) was kind enough to record a full Design Review video for this…but technical difficulties (aka I’m still new to OBS Studio) meant none of his audio was captured…oops…I am curious if people would actually be interested in these sorts of Design Review videos, any opinions or suggestions would be much appreciated!

Parts List

Printed Parts:

I’ve now made a handful of these valves, and I’ve made all of them from Overture PETG. I generally like working with PETG, and it holds up well for these. The only downside is that PETG does wear a bit at the contact between the drum and the steel balls. I haven’t experienced any problems, but I anticipate it will lead to progressively worse sealing over time. I didn’t want to use PLA because I expect mine to see a fair bit of UV exposure, but I’d be quite curious to hear what else folks try and what works well.

  • DrumCam.stl
  • Housing.stl
  • CamSupport.stl
  • ServoInterface.stl
Two full valve assemblies' worth of parts.

Please note, I sliced/printed these prior to the release of organic supports in Prusa Slicer, of which I am a very big fan. If I were printing these today I would use organic supports…and actually, I just realized that for the build I did in the images below, I did indeed slice it with them. But the screenshot I saved, is the screenshot I saved!

COTS parts

  • (Qty 2) 608 2RS Bearings — Aka skate board bearings. There’s not much demand on these bearings unless you’re putting yours in some weird/harsh environment, so any 8x22x7mm bearing should do fine.
  • (Qty 1) DS3225 Servo — It was originally designed for, and still can be built with, an MG995 servo, but while it seemed to operate fine for several weeks, I felt like it sounded like it was loading closer to stall than I wanted.
  • (Qty 8) 1/2" or 12.5mm balls — I have just been buying these in different sizes recently, but you obviously don’t need 100 pieces for this project.
  • (Qty ?) 5mm x 8mm Silicone Tubing — You’re looking for a compliant/soft tubing with the matching ID/OD. You would probably be fine (and maybe even get slightly better sealing) with a thicker wall, but at the cost of more Cam wear.
  • (Qty 4) M4 x 8.1 Heat set inserts — You should be able to use any length of M4 insert, just make sure to choose the corresponding fastener accordingly.
  • (Qty 1) M5 x 9.5 Heat set insert — This will be the load path from the servo to the camshaft, so just make sure you have enough thread engagement, but with it being M5, really any depth of insert should be fine.
  • There are a number of options for fasteners, and I tend to just use assorted kits for each size, which is overkill for the few fasteners you’ll need for this. So I’ll list them here
  • (Qty 4) m4 x 10 BHCS
  • (Qty 1) m5 x 30 BHCS — could also sub this with an m4x30 and replace one of the m5 nuts with an m4 nut, but may want to also toss in a washer just to be safe.
  • (Qty 2) m5 x 18 BHCS
  • (Qty 3) m5 hex nuts

Assembly

Get all of the printed parts
 
 
Remove the supports
 
 
Get the DrumCam and 608 2RS bearings
 
 
Press one bearing into each side. Here I’m using additional bearings just as spacers for the press. Depending on your print settings, you shouldn’t need anywhere near an arbor press for this, but I’m lazy.
 
 
Melt the M5 insert into the hole in the DrumCam (see below picture for additional clarity)
 
 
DrumCam with heat set insert and bearings installed.
Get M4 inserts and Housing.
Melt in M4s for Servo mount
Now get your 1/2"/12.5mm balls
Drop 2 balls into each bore in the Housing and get the DrumCam
Slide the DrumCam onto the post on the Housing with the M5 insert facing the servo mount
 
 
Attach the ServoMount. First insert the M5 nuts into the hex recesses in the housing (not visible from this view)
 
 
Now get your servo, servo horn, mounting hardware, and ServoHornInterface.
 
 
Attach the servo horn to the servo. You’ll want to power up the servo and set the position to Zero degrees (or whatever you decide on, but you’ll need your code and this alignment to match up!)
 
 
Attach ServoHornInterface to Servo Horn
 
 
Attach servo to Housing with M4 fasteners and then connect ServoHornInterface to DrumCam with M5

This project is part of a collection of AgTech projects that I am working on putting together as an open source hardware project, JFS Agri. I am excited by the intersection of growing my own food and playing with tech toys :) if you’d like to see a summary of the projects along the way, I’ve started an overview page here. I’d love to find like-minded folks with a similar interest that are interested in collaborating, generating data, or just chatting about AgTech!