Axial Swash Plate Feed Pump

[Toymaker]

I completed the last piece, which I've named the Channel Plate, as it contains the two ring-shaped channels; the outer ring channel connects the water input side of all 9 pistons, while the inner ring channel connects all 9 piston outputs. The channels are isolated from each other, and the outside world, by 3 O-rings.

Input & output connecters are shown in the photo below. I needed to counter-sink the socket head screws to avoid interfering with both connecters.

I still have a few more small machining tasks to accomplish, such as cut an O-ring channel inside the tubular housing which will seal the oil pool around the piston block, and install a plug in the valve plate. Then, finally, I can assemble all the pieces and begin testing my little toy.

 

[Toymaker]

Success ! After fixing a couple mistakes, my Mini Axial Feed Pump - V2 is now pumping water. In the video, the small, clear plastic container, the one that falls at the end of the video, holds 550 ml and is drained rather quickly by the pump. As with the previous test on the first pump version, I'm turning the pump with my cordless electric drill. Because some outer case dimensions changed from version 1, I need to re-make or at least modify the bracket which holds and connects the pump to the gear motor; once that task is completed, I can run some meaningful flow and pressure tests. But for now,...I'm satisfied.

One of the initial problems I needed to solve turned out to be too much spring force pushing against the inlet valve balls, preventing water from passing through the valve. Once I cut the springs length such that they now merely hold the balls in place without any pressure, the pump began working. Troll, is this ultra-low force against the ball inside the valve typical, or is this unique to my feed pump due to it's small size?

 

[The Ignoble Troll]

If I understand the issue youve stated correctly, no that's not uncommon. Inlet springs in pressure washer pumps are often mated to large faced poppet valves. Large face valves allow higher flow but also decrease the hydraulic pressure for them to open. The problem of those pumps not siphoning or being readily starved by low feed pressure all point to low induction ability.

Really all those springs need to be capable of is holding the valve in place to resist the high pressure wave when it comes.

If I turn a flooded axial 3200psi pump (just what I have on hand) with a thumb on the intake, the pump feels partially seized and has no detectable vacuum on my thumb, so those valves are not opening. When I toss it on the motor and supply pressurized feed water, it morphs into a thirsty beast.


Is this at all helpful?

 

[The Ignoble Troll]

Pump looks fantastic by the way.

 

[Toymaker]

If I understand the issue youve stated correctly, no that's not uncommon. Inlet springs in pressure washer pumps are often mated to large faced poppet valves. Large face valves allow higher flow but also decrease the hydraulic pressure for them to open. The problem of those pumps not siphoning or being readily starved by low feed pressure all point to low induction ability.

Really all those springs need to be capable of is holding the valve in place to resist the high pressure wave when it comes.

If I turn a flooded axial 3200psi pump (just what I have on hand) with a thumb on the intake, the pump feels partially seized and has no detectable vacuum on my thumb, so those valves are not opening. When I toss it on the motor and supply pressurized feed water, it morphs into a thirsty beast.


Is this at all helpful?

Yes, quite helpful, thank you.

This newer, ball-valve version doesn't siphon near as well as the previous rotating plate valve version.
If I prime the pump by forcing enough water through the intake line to fill the pump with water, it siphons OK. But if I leave the pump and intake line filled with only air, it wont pull the water up through the intake tube.

I'll learn a lot more after I connect the gear motor to the pump and I can control the pump's rpm much better.

 

[The Ignoble Troll]

Even products to condition pump seals are ether pressurized or in squeeze bottle, because the vacuum is so anemic

https://simpsoncleaning.com/products/pump-guard-80273/


I think you just need a booster pump.

But it certainly looks like you are on the right track.

 

[The Ignoble Troll]

Will you have room to add a pulley between the motor and the pump? Just thinking that you could drive an automotive coolant pump in tandem. Don't those see high temperatures?

 

[Toymaker]

Will you have room to add a pulley between the motor and the pump? Just thinking that you could drive an automotive coolant pump in tandem. Don't those see high temperatures?

I didn't make room for a pully to drive a separate pump, but I made an all aluminum centrifugal pump that can be driven by a separate electric motor which will work if I need it. Until I start using hot water through the feedpump, I have an RO pump with rated flow of 5.3 L/m at 150 psi,...again, only if I need it.

 

[Toymaker]

I have some initial test results from the final assembly, with pics and video of course

Below is what I hope will be the final assembly; still lots of testing needed, and maybe a few problems to resolve, before I give it my seal of approval.

The good news is that it siphons much better with the final motor, though not nearly as well as the valve plate version; I may not need a boost pump,...time will tell.

By using 9 pistons I was expecting much smoother pressure output, but as the video below shows, as pressure approaches 60 psi, the meter becomes unreadable. I'm guessing that I might have one or more inlet ball valves not opening. I measured 3 LPM open flow at max rpm, now I need to measure the max rpm and calculate what the flow rate should be.

If the pulses don't go away, I have an oil-filled guage on the boiler stand,...I'll try using that to see if the pressure becomes readable.

 

[Toymaker]

Testing Update: Measured rpm with open flow is nearly 2000 rpm, which is nearly twice what I expected, and what I designed for. At a measured 1000 rpm the open flow is only 1.7 LPM; it should be 3 LPM. Seems something wonky is still going on with my valves,...one or more valves are either not opening completely or not fully closing.

Theory: Since I'm using steel balls seating against a 6061 aluminum housing, during the high pressure output cycle, as each steel ball slams against the aluminum seat, the softer aluminum should begin to conform to the rounded ball shape thereby creating a tighter seal. Therefore, a break-in period should be helpful. At least, that's my theory.

 

[The Ignoble Troll]

Testing Update: Measured rpm with open flow is nearly 2000 rpm, which is nearly twice what I expected, and what I designed for. At a measured 1000 rpm the open flow is only 1.7 LPM; it should be 3 LPM. Seems something wonky is still going on with my valves,...one or more valves are either not opening completely or not fully closing.

Theory: Since I'm using steel balls seating against a 6061 aluminum housing, during the high pressure output cycle, as each steel ball slams against the aluminum seat, the softer aluminum should begin to conform to the rounded ball shape thereby creating a tighter seal. Therefore, a break-in period should be helpful. At least, that's my theory.

Have you tried it with a dummy load and pressure gauge?

If all the balls are closing the pressure gauge, at least a glycerine filled one, should shiver around an output pressure reading but if you have some missed ball seating events, then it should oscillate more wildly.

If you throw a valve and gauge onto the end of your pressure washing hose, the hose should provide some dampening for your air filled gauge.

 

[Toymaker]

Have you tried it with a dummy load and pressure gauge?

If all the balls are closing the pressure gauge, at least a glycerine filled one, should shiver around an output pressure reading but if you have some missed ball seating events, then it should oscillate more wildly.

If you throw a valve and gauge onto the end of your pressure washing hose, the hose should provide some dampening for your air filled gauge.

My dummy load is the small valve, mostly hidden by my hand, in the video in post #69. In the video, I'm slowly closing that valve.

 

[The Ignoble Troll]

Oops, sorry. I missed the video because I replied from reading the emailed update.

I see, looks to me like you are right. Some balls are not behaving. I wonder if it is their inertia

 

[The Ignoble Troll]

Are you able to remove the pressure gauge, leaving the valve set, and try running it in? Maybe it just needs some time to bed?

 

[Toymaker]

Are you able to remove the pressure gauge, leaving the valve set, and try running it in? Maybe it just needs some time to bed?

My thoughts as well; the steel balls being slammed into the much softer 6061 drilled aluminum seat should eventually form a nicely rounded concave seat in the aluminum, which should seal much better. I should be able to hasten that process by disassembling the valve plate and gently hand hammering the steel balls into the aluminum. Also, the current steel balls I'm using are mild steel balls made for air-soft toy guns, which will rust rather quickly,...so I ordered Silicon Nitride ceramic balls, which should be much more uniformly round, and never rust.

Also, I ordered new, hopefully much weaker, springs to push the balls closed. The current springs were scavenged out of ball-point pens and will likely rust. The replacement springs are 304 stainless.

 

[Toymaker]

I replaced the 0 to 160 psi pressure guage with a liquid-filled 0 to 870 psi guage.

Readings from 0 through 100 psi were remarkably smooth, but by the time I reached 200 psi the needle was bouncing around a bit, swinging +/- about 30 psi. At that pressure, 200 psi, the electric motor was struggling to run and had become alarmingly HOT. I need to replace the motor & geared speed reducer with a much larger unit.

I placed an order today for a larger motor with speed reducer, but the ETA is 3 weeks.

 

[The Ignoble Troll]

I replaced the 0 to 160 psi pressure guage with a liquid-filled 0 to 870 psi guage.

Readings from 0 through 100 psi were remarkably smooth, but by the time I reached 200 psi the needle was bouncing around a bit, swinging +/- about 30 psi. At that pressure, 200 psi, the electric motor was struggling to run and had become alarmingly HOT. I need to replace the motor & geared speed reducer with a much larger unit.

I placed an order today for a larger motor with speed reducer, but the ETA is 3 weeks.

Hey, that sounds like some solid progress though.

Are you going to try your boiler under 100PSI at a lower burner setting?

Be really neat to see what the turbine does at an available 100psi of steam.

What flow rate did you achieve? Enough to spin up the turbine?


Nice call on the ceramic balls, I've never seen ceramic ball check valves, just stainless, so it will be neat to see how they hold up.

 

[Toymaker]

Hey, that sounds like some solid progress though.

Are you going to try your boiler under 100PSI at a lower burner setting?

Be really neat to see what the turbine does at an available 100psi of steam.

What flow rate did you achieve? Enough to spin up the turbine?


Nice call on the ceramic balls, I've never seen ceramic ball check valves, just stainless, so it will be neat to see how they hold up.

Because the electric motor was becoming scorching HOT, I didn't take the time to measure flow rate, but it was very small as the motor had slowed considerably.

Using this feed pump, with it's current anemic motor, to move water through the boiler would be far too risky; if the motor were to overheat and fail, I risk running the boiler tubes dry. Yes, the computer should sense the pressure drop and quickly shut down the burner,....but there's no good reason to take that risk. Better to wait a few weeks for the much more capable motor (5 times the torque) to arrive.

 

[The Ignoble Troll]

It's a fixed displacement pump, so if you took a flow reading at 0psi then 100psi then 200psi, with cool down breaks in between, then you should be able to quickly calculate rpm vs displacement at each pressure point.

Sounds like 0psi and 100psi had proper valve action, so they should work out to the same volume/rpm

At 200psi it sounds like it will have a reduced flow so volume/rpm/# of pistons = ~missed valve closings.

Right? It makes sense in my head at least.

If the difference between the flow rates does not easily divide into the number of pistons, you could inference that it is partial valve closings that are messing it up.


All this is assuming the motor can push at least a half liter before getting too hot.

 

[Toymaker]

I definatly have valve issues,...at least at low rpm. Watch the air bubbles in the output line,...they're pulsing through the line and appear to stop or even reverse direction very briefly. I'm not sure if this indicates valve(s) not opening, or not fully closing.

Your logic concerning fixed displacement pumps seems sound. I used an online calculator to determine total displacement: Engine Displacement Calculator which is 2.988 CC. At 1000 rpm, regardless of pressure, the pump should be pushing out 3 liters/minute, the problem is maintaining RPM as the pressure increases.