How to build a barrel pump
I saw a post a while back about making a barrel pump and I thought I'd show you how I make mine. I've made more than a few and it is much easier if you and some friends decide you want one because they are labor intensive but they are pretty simple to make. You need a drill press and an adjustable hole saw like you see in the first picture. I made a 6" pump this time, but a 4" is the same. It is helpful to make test cuts with the hole saw because they are hard to adjust. The plastic I like to use is 1/4" vinyl (vinyl may be measured in metric). I've also used HDPE but it is a bit soft.
First you need to adjust the cutter so that you cut 1 circle that fits snugly in the pipe, and then 1 circle that is about 1/16" or 3/32" looser. The snug circle will have 4 circles cut out of it. This holds the gasket as the pump is drawn up and allows air to go around the gasket. The loose circle holds the gasket as the pump goes down and seals against the plunger and the walls. You need some space so that the air can go around the disk on the up stroke. These are assembled with a 1/4" SS bolt with a nylock nut for a spacer between the 2 disks and are bolted to a 1 1/4" pvc schedule 40 end cap. It is helpful if you use a cap that is flat and not round. I get the flat ones at Sutherlands. (pictures 2 and 3)
The end caps are 6" DWV caps. The pipe I use is SDR 35 DWV. A hole is cut to accept a 1" slip x 3/4" threaded coupler in the side of the cap that forms the bottom. For the top the hole saw is adjusted again to create another vinyl disk that fits tightly inside the cap. Then the saw is adjusted again and a hole is made for a 1 1/4" pipe to slide through the center. I cut the cap and the vinyl at the same time to help keep the hole centered. 2 holes are cut in the side for a handle and to allow air to enter the pump. I use a forstner bit or a spade bit for these holes. (picture 4)
The hose is attached using the 1" slip x 3/4" threaded coupler which is pushed through the hole in the bottom cap (I make mine snug) and then I have cut in half a 1" slip coupler. This coupler conveniently also fits inside of my check valve which is a dishwasher drain valve. Try a couple of couplers or you may have to sand the outside of the coupler. (picture 5) A notch is then cut in the pipe so that it fits over the check valve/hose assembly. (picture 6)
To make the gaskets I made 2 identical disks out of vinyl with the hole saw that are a bit larger than the bore of the pipe. I use craft foam and use a 1/4" bolt to sandwich the foam between the disks. I spin this on a drill and use a razor blade to make a smooth cut. I then use 2 smaller disks and a 1/4" bolt and repeat to make the o-ring hollow. If you look close you can see the outline of the barrel. Pictures 7 and 8
I then test the pump and then glue everything together. Make a handle out of 1 1/4" schedule 40 pvc pipe but I use a 1 1/4" schedule 80 T for the handle. I use a 3/4" ID vinyl vacuum hose and a 3/4 threaded to 3/4" barbed 90 elbow
The last 2 pictures are probably bit but they show the gasket in place and they also show a finished 4" pump. I use an abs cap for the bottom because they are flat and all of the DWV caps that are 4" have been round. There is an adapter for the DWV pvc pipe to ABS. it is white and a little of it can be seen in the picture. There is special cement for ABS to PVC that I use but these don't hold much pressure.
Hope this helps.