Axial Swash Plate Feed Pump

[Toymaker]

I've decided to build from scratch a small 9-piston feed pump similar to this drawing:

Design Goals: 3 LPM (Liters Per Minute) at greater than 600 psi
9 pistons with 8mm diameter
Stroke of each piston: 0.26"
Total displacement: 0.182 cubic inches (0.003 Liters)
1000 RPM
Driven by a fractional HP geared motor (think cordless electric drill)

My working drawing is below.
Valve plate, port plate, cylinder block, pistons, swash plate are all made from brass.
Each piston has an O-ring to help with sealing.

My biggest design concern: will the use of brass provide low sliding friction without galling and only water as lubrication?
Much more to follow.

 

[The Ignoble Troll]

I can not wait to see how this develops. Talk about a bespoke system!

 

[Toymaker]

I started machining pieces about a week ago, just to see if I could make some of what I believed would be the more difficult parts for me to fabricate. So far, I'm on a roll, and most everything is working to plan.

All the parts in the pic below are either brass or stainless. I like using O-rings wherever I can instead of gaskets or silicone sealant; the bottom pic shows O-rings around the input and output ports, and seals against the yet-to-be-made aluminum housing.

To give readers an idea of scale: the cylinder block (holds the pistons) is 1.8" in diameter and 1.3" long. I tried making the port plate and cylinder block as one piece, but found that made polishing those 9 cylinder walls, at the deep end, to be beyond my capabilities. So I opted for a separate piece.

 

[Toymaker]

Made & assembled a few more parts.
The shiny ball-head screws were purchased via AliExpress, 15 pcs for $5.38.

The pistons were made from some 8mm brass stock I had left over and lying in my spare parts bin; the finish is pretty ugly, and I'm hoping the O-rings take up the slack to prevent leaks,...if not, I'll need to make tighter fitting pistons from some larger stock.

The retaining plate is pushed away from the the cylinder block via a spring located around the drive shaft and inside the block; it sits on a ball-shaped brass push rod which the spring pushes against, (I updated the drawing in post #1 show this part)

The thin retaining plate still needs a little machining on the slots where the ball-screws fit; ideally those slots should have half-round surfaces where the bottom of the balls sit, which will allow for a greater angle of the retaining plate.
That milling is waiting on a ball-nose milling bit to arrive in the mail.

Judging by the air pressure I get when I push down on any single piston, I'm confident it will pump water when finished, but will it leak between the port plate and the valve plate? And how much pressure will it make?

 

[peterl95124]

FYI, I made something similar a while ago, the one troubling thing I noticed is that where the cylinder pushes against the valve plate both end up with scoring and abrasion, brass-on-brass it seems is the worst possible choice for bearing materials (even when lubricated). I am planning on replacing the valve plate in mine with teflon (and hoping I can polish out the scoring on the cylinder without loosing much dimensionally) ...

 

[The Ignoble Troll]

FYI, I made something similar a while ago, the one troubling thing I noticed is that where the cylinder pushes against the valve plate both end up with scoring and abrasion, brass-on-brass it seems is the worst possible choice for bearing materials (even when lubricated). I am planning on replacing the valve plate in mine with teflon (and hoping I can polish out the scoring on the cylinder without loosing much dimensionally) ...

If you have space, maybe you could bore out the cylinders a little and add a packing at the swash plate end of the pistons to convert the whole thing to a plunger pump. Then the sealing/friction is localized to the packing.

They do this with very high pressure triplex pumps.

 

[peterl95124]

If you have space, maybe you could bore out the cylinders a little and add a packing at the swash plate end of the pistons to convert the whole thing to a plunger pump. Then the sealing/friction is localized to the packing.

They do this with very high pressure triplex pumps.

I'm not talking about the pistons, I'm talking about the *rotary-valve* that these rotating-cylinder swash-plate type pumps have

 

[tractor162003]

OK where is the (View attachment 156826) from post # 1. When I click on it , it said cannot be found.

Tom

 

[Toymaker]

OK where is the (View attachment 156826) from post # 1. When I click on it , it said cannot be found.

Tom

I uploaded that jpg file again; hopefully everyone can see it now.

 

[Toymaker]

FYI, I made something similar a while ago, the one troubling thing I noticed is that where the cylinder pushes against the valve plate both end up with scoring and abrasion, brass-on-brass it seems is the worst possible choice for bearing materials (even when lubricated). I am planning on replacing the valve plate in mine with teflon (and hoping I can polish out the scoring on the cylinder without loosing much dimensionally) ...

Post a picture or two or three,....I'ld love to see your build. What is you pump pumping?

Google searches found conflicting reports as to whether or not, brass is classified as a self lubricating metal, but when I Google, "brass bearings" I find lots of plain brass bearings are available for purchase. Also from my own experience, I still see many electric motors use brass or bronze bearings. Yes, I'm still concerned abut galling between the port plate and the valve plate, but if that occurs in my pump, both of those parts are easily re-made and replaced.

If my brass plates self destruct, my plan B is to make both plates from aluminum and have the plates Type III hard coat anodized. Type III anodize is a ceramic coating (aluminum oxide), and like ceramic bearings, when two type III anodized parts slide against each other, it's almost frictionless. Plan C is to machine both plates from aluminum oxide discs, which are available on eBay and AliExpress at reasonable costs. Aluminum oxide discs are likely the best technical solution, but would be painfully slow to machine as it requires diamond bits to grind away material.

Good luck with your Teflon valve plate.

 

[The Ignoble Troll]

Electrical brass is specially formulated to resist wear and pitting from arcing iirc

 

[Toymaker]

Electrical brass is specially formulated to resist wear and pitting from arcing iirc

Thanks for the idea,....but,...

During my web searches I found several bearing manufacturers boasting their use of a brass-graphite alloy,...but when I try to find a shop that sells this slippery alloy metal, I cannot.

 

[petertha]

That's really cool. So you mean you are will be making little feet like sketch with a ball socket on one side & flat on the other once your ball end mill arrives?
Are the ball ends sourced from RC car/heli/plane application? Reason I ask is I seem to recall some/most? are turned from a native material & others are plated if that affects anything. What are you going to be pumping?

 

[Toymaker]

That's really cool. So you mean you are will be making little feet like sketch with a ball socket on one side & flat on the other once your ball end mill arrives?

The small size of the slippers (little feet) for my build, allows for a simpler design than shown in your drawing. All 9 should not be very difficult to make.

Are the ball ends sourced from RC car/heli/plane application? Reason I ask is I seem to recall some/most? are turned from a native material & others are plated if that affects anything.

Yes, the ball ends are sold for use on RC models and are most likely made from a common, cheap steel. I believe they will be strong enough in compression and tension.

What are you going to be pumping?

I'm building this to pump water into my monotube boiler.

 

[The Ignoble Troll]

Thanks for the idea,....but,...

During my web searches I found several bearing manufacturers boasting their use of a brass-graphite alloy,...but when I try to find a shop that sells this slippery alloy metal, I cannot.

Sorry, I meant that more as a factoid about the difference between the brass in say a commutator bar and a the stuff we get as machining stock. Sorry for the goose chase.

In the past I cut some electrical brass and found it machined differently from the regular golden stuff(tough as I recall), but at the time it was only available in bulk bar stock. Seems that hasn't changed. I think it was an alloy close to C220 that I was looking for... but not C220. Too long ago now.


This goes out of my field of knowledge but perhaps some steam oil would help your pump prevent wear.

It would be interesting to see how the turbine reacts to droplets of emulsified steam oil, or if it cared.


The Stanley steamer used an oil/steam seperator, as I fuzzly recall. That might be useful for you, if you do add lubercant.

Otherwise maybe you could adjust your water resivoir so that oil circulates and recycles continuously, like it would in an ORC(as I understand them).

You could probably test this by compounding some animal cooking fat with mineral oil. Mmm bacon for science.


If you clarified the fat by boiling over water, skimming and filtering - you should have something left over that approaches what they add to mineral oil to make steam oil (if my very fuzzy memory serves).


I wish you lived on the otherside of the pond and I could see this thing in person. I'm really rooting for you.

Thanks for sharing.
Your slipper engineering looks great!

Your initial turbine... how do you think it would work as a blower? Any chance of it getting re-included as the blower?

 

[Toymaker]

FYI, I made something similar a while ago, the one troubling thing I noticed is that where the cylinder pushes against the valve plate both end up with scoring and abrasion, brass-on-brass it seems is the worst possible choice for bearing materials (even when lubricated). I am planning on replacing the valve plate in mine with teflon (and hoping I can polish out the scoring on the cylinder without loosing much dimensionally) ...

Just found this video on YouTube showing brass valve plates being lapped and polished. Not a very exciting or informative video beyond it confirming that at least some commercial valve plates are made from brass.

Lapping Brass Valve Plates

Of course this doesn't guarantee that brass valve plates will survive pumping water, meaning I will need to find out for myself.

 

[Toymaker]

Sorry, I meant that more as a factoid about the difference between the brass in say a commutator bar and a the stuff we get as machining stock. Sorry for the goose chase.

In the past I cut some electrical brass and found it machined differently from the regular golden stuff(tough as I recall), but at the time it was only available in bulk bar stock. Seems that hasn't changed. I think it was an alloy close to C220 that I was looking for... but not C220. Too long ago now.


This goes out of my field of knowledge but perhaps some steam oil would help your pump prevent wear.

It would be interesting to see how the turbine reacts to droplets of emulsified steam oil, or if it cared.


The Stanley steamer used an oil/steam seperator, as I fuzzly recall. That might be useful for you, if you do add lubercant.

Otherwise maybe you could adjust your water resivoir so that oil circulates and recycles continuously, like it would in an ORC(as I understand them).

You could probably test this by compounding some animal cooking fat with mineral oil. Mmm bacon for science.


If you clarified the fat by boiling over water, skimming and filtering - you should have something left over that approaches what they add to mineral oil to make steam oil (if my very fuzzy memory serves).


I wish you lived on the otherside of the pond and I could see this thing in person. I'm really rooting for you.

Thanks for sharing.
Your slipper engineering looks great!

Your initial turbine... how do you think it would work as a blower? Any chance of it getting re-included as the blower?

My thoughts on lubricating additives for water that can survive the heat & pressure inside the boiler: common cutting fluids use in machine shops. Cutting fluids are mostly meant to cool the cutting bits, but they also provide significant lubrication, and they don't leave any solid residue behind when they evaporated off the high temperature of the cutting bit during milling or lathe work.

There's also a large steam car community in the US and Great Britain that mostly use piston engines,... engines that need lubrication, so surely this is a problem that already has been solved.

I plan to build a dedicated blower once I know more about the capabilities of the boiler,...how much steam will it actually produce at 500 psi ?

 

[petertha]

The pistons were made from some 8mm brass stock I had left over and lying in my spare parts bin; the finish is pretty ugly, and I'm hoping the O-rings take up the slack to prevent leaks,...if not, I'll need to make tighter fitting pistons from some larger stock.

Can you elaborate on piston / bore clearance? Is the main seal the (longish) piston or the O-ring itself? I got kind of lost in online calculators, but do you have a ballpark figure of what kind of pressure an O-ring can withstand in this size? I cant wait to see it run!

 

[The Ignoble Troll]

My thoughts on lubricating additives for water that can survive the heat & pressure inside the boiler: common cutting fluids use in machine shops. Cutting fluids are mostly meant to cool the cutting bits, but they also provide significant lubrication, and they don't leave any solid residue behind when they evaporated off the high temperature of the cutting bit during milling or lathe work.

There's also a large steam car community in the US and Great Britain that mostly use piston engines,... engines that need lubrication, so surely this is a problem that already has been solved.

I plan to build a dedicated blower once I know more about the capabilities of the boiler,...how much steam will it actually produce at 500 psi ?

For sure you can straight up buy steam oil.

Personally I'd avoid cutting fluid, they are formulated to make metals easier to cut ie. wear.

Check out this link

https://www.ghls.org/ghlsv1/reference-info/truth-about-steam-oil/


Also, as a side note, the special ingredient in many cutting/tapping oils/compounds are lard or tallow plus stuff like sulfur compounds which ease the cutting.

 

[Toymaker]

Can you elaborate on piston / bore clearance? Is the main seal the (longish) piston or the O-ring itself? I got kind of lost in online calculators, but do you have a ballpark figure of what kind of pressure an O-ring can withstand in this size? I cant wait to see it run!

There's between 0.005" and 0.010" of clearance between the piston OD and the cylinder ID, with most of the looseness coming from the pistons.

I haven't done any math calculations on O-ring clearance vs pressure, however, I'm confident the O-rings can easily hold the 800 psi which is what I expect to be the pump max working pressure. Most pressure washer fittings connect the same way as my piston O-rings, and their clearances are typically 0.030" or more and retain pressures over 3000 psi.

Here's a photo of a typical quick connect high pressure fitting; notice the O-ring is the main seal.