Mini diesel engine.

[Nerd1000]

Some semantics here. To me a plunger pump is one with the seal is where the piston enters the cylinder. This is probably not suitable for fuel injection due to the likely hood of air being trapped around the piston. A piston pump is where the seal is at or close to the end of the piston which is generally how fuel injection pumps are made.

My thinking is pretty much the same. Though here's a question, where is the seal on a pump which works by having a very tight clearance between a long cylindrical piston and its mating cylinder, like one of your injection pumps?

 

[Roger B]

I think that the seal is at the end of the piston. As soon as the inlet port is closed by the piston the pressure starts to rise. In the case of my helix pumps the seal is just the active land of the helix, not the full length of the plunger.

 

[minh-thanh]

You have experience with engine cylinders, pump cylinders are no different. Same . It's just smaller - a little more difficult to do.

 

[The Ignoble Troll]

Some semantics here. To me a plunger pump is one with the seal is where the piston enters the cylinder. This is probably not suitable for fuel injection due to the likely hood of air being trapped around the piston. A piston pump is where the seal is at or close to the end of the piston which is generally how fuel injection pumps are made.

No semantics intended. Both pumps are used for this purpose and I'd just like verification on which they are using to help in planning my own mini hydraulic injector for a different project.

 

[Roger B]

I think the difference may be related to strokes and volumes. My injection pumps have a 2mm bore and a typical working stroke of a fraction of a mm. In this case any trapped gas volume will cause problems so the seal must be at the top of the piston. If the working stroke is several times the bore diameter then a plunger pump with a seal/gland at the entrance to the cylinder will be fine.

 

[Lloyd-ss]

I have tried making several kinds of pumps with seals (and no seals) in all different locations. Based on my success rate, they all fall in one class, for semantics sake, : PITAs.

Without having a factory of specialized precision equipment, even if you do the very best you can, there is still quite a bit of luck necessary to be successful. Any seals that are utilized such that they are compressed during each stroke are not likely to work. At least for me. Starting with a factory pump element removes a lot of the stress of building the pump. I tried a couple of factory elements and the fit and finish, and the FUNCTION, was so much better than anything I built myself. And if it helps you get your engine working, that is a whole lot better than endless frustration and lost time. Just my opinion.

 

[The Ignoble Troll]

That's more then fair.

When I regain access to my lathe I want to try a true self purging plunger pump with a solid teflon or HDPE packing + nut.

Boiler feed pump type design. I'm optimistic that reducing the metal on metal sealing will increase success.


Can't fault the path of using an off the shelf part. Whatever makes the hobby more enjoyable

 

[minh-thanh]

Starting with a factory pump element removes a lot of the stress of building the pump. I tried a couple of factory elements and the fit and finish, and the FUNCTION, was so much better than anything I built myself. And if it helps you get your engine working, that is a whole lot better than endless frustration and lost time. Just my opinion.

Even though I do everything myself...but I like your way of thinking. Still my saying: Get the engine running, everything else will follow . At least, that engine tells you what you should do next, perfect it,...

 

[The Ignoble Troll]

Even though I do everything myself...but I like your way of thinking. Still my saying: Get the engine running, everything else will follow . At least, that engine tells you what you should do next, perfect it,...

And you have incredible patience for doing so!


I've never seen an IC engine, like this, that was designed so organically

 

[Roger B]

Without having a factory of specialized precision equipment, even if you do the very best you can, there is still quite a bit of luck necessary to be successful. Any seals that are utilized such that they are compressed during each stroke are not likely to work. At least for me. Starting with a factory pump element removes a lot of the stress of building the pump. I tried a couple of factory elements and the fit and finish, and the FUNCTION, was so much better than anything I built myself. And if it helps you get your engine working, that is a whole lot better than endless frustration and lost time. Just my opinion.

There was nothing available commercially in the sizes I needed so I decided to do it the hard way, learning how to deep drill, ream and lap with a series of experiments. Avoiding bell mouthing is quite an art although the problem can be reduced by making the cylinder a bit longer than required and then cutting the bell mouth off. This then increases the deep drilling depth I gave up trying to lap my own plungers/pistons from hardened silver steel after having received a trilobed piece and now use cut down commercial pin gauges with the helix ground in. It can be done with just a second-hand Hobbymat and a Proxxon hand grinder.

 

[The Ignoble Troll]

Nice solution to the helix