Monotube Flash Boiler Design

[Toymaker]

That's practically zen.

What about also getting the drill style one and reverse engineering it?

I will wait for the bright red more powerful washer to arrive, and when it does, I can ***** the build quality of the pump, hook it up and see how well it performs on my boiler. If I'm really lucky, reverse engineering wont be necessary. Thinking ahead, these pumps are so small, light, and inexpensive that I could afford to put two in parallel if I need the additional flow rate.

 

[The Ignoble Troll]

Just curious, after seeing your air pump build, why not repeat your success and do a water pump build? If you can do such a great job on a swashplate compressor, then a swash plate, or easier/better, triplex pump should be a breeze.


A triplex with ball bearing shaft supports, an external unloader and oversized off the shelf valves - would readily lend itself to your creation.

The improved oil sump on a triplex would also lend itself to adding oil cooling/filtering down the road. Cool clean oil would make the thing last a very long time.

Off the shelf valves are cheap and oversizing them will increase longevity while increasing pump efficiency.

Cheap Axial pumps are rated in >tens< of hours. Good ones maybe might be rated to 50 hours.

A decent triplex pump is rated in the hundreds of hours and a really good one is rated in the thousands of hours.


Seeing your machining I have total faith in your ability to whip up a long lasting perfectly sized triplex and of course... ...to post build pictures!

There is very little to them. Much simpler then a swash air pump.

 

[Toymaker]

Just curious, after seeing your air pump build, why not repeat your success and do a water pump build? If you can do such a great job on a swashplate compressor, then a swash plate, or easier/better, triplex pump should be a breeze.


A triplex with ball bearing shaft supports, an external unloader and oversized off the shelf valves - would readily lend itself to your creation.

The improved oil sump on a triplex would also lend itself to adding oil cooling/filtering down the road. Cool clean oil would make the thing last a very long time.

Off the shelf valves are cheap and oversizing them will increase longevity while increasing pump efficiency.

Cheap Axial pumps are rated in >tens< of hours. Good ones maybe might be rated to 50 hours.

A decent triplex pump is rated in the hundreds of hours and a really good one is rated in the thousands of hours.


Seeing your machining I have total faith in your ability to whip up a long lasting perfectly sized triplex and of course... ...to post build pictures!

There is very little to them. Much simpler then a swash air pump.

I very much appreciate your faith in my machining abilities, and I did spend more than a few minutes seriously considering building my own pump,....even went so far as to check what Aluminum stock I have, and was it the right size. Even drew up a few rough pencil sketches.
In the end, my decision to buy instead of build is based mostly on the amount of work I still need to do on all the other pieces and parts that still need made and assembled.

 

[Toymaker]

Using a Cordless Pressure Washer as a feed pump.

The more powerful washer arrived today and I can report that it seems suitable for my needs. Flow rate with a pressure nozzle installed is an impressive 5 LPM,...it's advertised for 4.1.

Reading the pressure is a guess-tament as the needle on the dial guage is pulsing wildly; middle of the pulse is about 600 psi, with peaks that appeared to exceed the 60 Bar (875 psi) limit of the guage. The advertisement claims 100 Bar,....honestly, I don't know if it made that or not.

Removing the pump & motor assembly shows the pump body is all plastic, but at least the cylinder and piston inside the plastic body are metal. Will this pump be able to handle 100 C water? Time and testing will tell.

I'm impressed with the small motor, which is marked: 18 V. Advertisements claim 600 Watt, which at 18V would mean the battery would need to supply 33 amps!! Not Likely.

I will need to plumb this little pump into the boiler to continue testing.

 

[The Ignoble Troll]

No, valve damage starts at a bit over 53°C and happens exponentially as tempurature increases.


For a pump that can build both pressure and required flow, you will need a high end pump.


Or maybe throw together a plunger style pump and then you have no pistons to worry about.

 

[NapierDeltic]

Hi Toymaker. I know this type of motor. 600W might not be continuous power. But I think with additional cooling it can cope.

 

[Toymaker]

No, valve damage starts at a bit over 53°C and happens exponentially as tempurature increases.

Doesn't this depend on the type of plastic used, and it's CST (Continuous Service Temperature) ? Per this CST list, most plastics have a CST above 100 C, only a few are rated below 100 C. Since I have no way to find out which plastics are used to make this pump, seems testing at increasing temperatures is the only way to know with certainty; Yes?

For a pump that can build both pressure and required flow, you will need a high end pump.

The first 2 tests I performed were to measure flow rate by timing how fast the pump could empty a 2 litter container; this test was done with the pump assembly still inside the pressure washer. The first test was done without a spray nozzle, so zero pressure output. The second test was done with a pressure nozzle installed; this nozzle has a 0.050" diameter hole. Both tests results were the same: 5 LPM flow. Per this online Flow Rate thru an Orifice calculator, this pump is delivering 54 BarG (783 psig). Now, to be fair, I'm sure a high-end pump will last much longer, and be able to handle 100 C water with no problem, but for $33.00, this little pressure washer pump will do nicely

The 3rd test I performed was to pressure-wash a small section of concrete patio, which it easily cleaned. It typically takes over 800 psi to clean concrete. Certainly not an accurate way to measure pressure, but it gave me a ball-park idea of what pressure the pump was delivering.

For the final test, I cobbled together enough plumbing connectors, (with lots of small leaks) to attach a dial pressure guage, which read something over 600 psi. The guage is oil-filled and still the needle jumped so rapidly as to be nearly invisible. I'm hopeful the boiler tubing will act as a pressure accumulator and result in a more steady pressure that I can read; I will keep you posted.

Or maybe throw together a plunger style pump and then you have no pistons to worry about.

OK, I'm still learning the difference between piston and plunger pumps, but after a bit of Googling, I believe this pressure washer pump is a plunger type, as the seals around either end of the plunger are held stationary by the pump body.

 

[The Ignoble Troll]

Doesn't this depend on the type of plastic used, and it's CST (Continuous Service Temperature) ? Per this CST list, most plastics have a CST above 100 C, only a few are rated below 100 C. Since I have no way to find out which plastics are used to make this pump, seems testing at increasing temperatures is the only way to know with certainty; Yes?



The first 2 tests I performed were to measure flow rate by timing how fast the pump could empty a 2 litter container; this test was done with the pump assembly still inside the pressure washer. The first test was done without a spray nozzle, so zero pressure output. The second test was done with a pressure nozzle installed; this nozzle has a 0.050" diameter hole. Both tests results were the same: 5 LPM flow. Per this online Flow Rate thru an Orifice calculator, this pump is delivering 54 BarG (783 psig). Now, to be fair, I'm sure a high-end pump will last much longer, and be able to handle 100 C water with no problem, but for $33.00, this little pressure washer pump will do nicely

The 3rd test I performed was to pressure-wash a small section of concrete patio, which it easily cleaned. It typically takes over 800 psi to clean concrete. Certainly not an accurate way to measure pressure, but it gave me a ball-park idea of what pressure the pump was delivering.

For the final test, I cobbled together enough plumbing connectors, (with lots of small leaks) to attach a dial pressure guage, which read something over 600 psi. The guage is oil-filled and still the needle jumped so rapidly as to be nearly invisible. I'm hopeful the boiler tubing will act as a pressure accumulator and result in a more steady pressure that I can read; I will keep you posted.


OK, I'm still learning the difference between piston and plunger pumps, but after a bit of Googling, I believe this pressure washer pump is a plunger type, as the seals around either end of the plunger are held stationary by the pump body.

You cann test for sure but the sharp swing from vacuum to high pressure conditions, destroys the stuff.

That's why when they build heated pressure washers, the pump goes before the water heater, even though that means coils of water at raised °C vs heating the water and then pumping it.

 

[Toymaker]

You cann test for sure but the sharp swing from vacuum to high pressure conditions, destroys the stuff.

That's why when they build heated pressure washers, the pump goes before the water heater, even though that means coils of water at raised °C vs heating the water and then pumping it.

I'm guessing the first sign of failure will be reduced pressure and flow rate at all RPMs ? Or, leaks around the seams between pump-body parts that are screwed together ?

 

[The Ignoble Troll]

I'm guessing the first sign of failure will be reduced pressure and flow rate at all RPMs ? Or, leaks around the seams between pump-body parts that are screwed together ?

You'll usually hear it and then see pressure drop. Sorta a rough noise.


I've got my fingers crossed that it will work for you.


If the pistons and cylinders hold up, maybe you can shoe horn in some metal valves like spring loaded ball check valves.


If the valve seats are somewhat conventional, maybe metal after market stuff would help

Ultimate Washer Replacement for General Pump Check Valves KIT001 Kit 1 New Valves + O-Rings https://a.co/d/0bWKA0p


Either way if there is anything I can help source or w/e, let me know.



For pressure all you need is a check valve, ball or needle valve and a pressure gauge. Arrange the flow so the pressure spikes are trapped by the check valve to give you peak psi ratings at the gauge.

The valve is just to release pressure.

 

[Toymaker]

I finished plumbing in the tiny pressure washer pump and ran a few initial tests. I'm being very cautious because I don't want to burn out the tiny motor, which is rated for 18 vdc, and I'm giving it twice that (36 vdc) via a PWM (Pulse Width Modulation) motor driver. With the PWM set to 30% , I slowly closed the steam output valve to reduce the orifice size the pumped water was being forced thru, resulting in higher pressure from the pump. As pressure increased, motor RPM decreased and pressure pulses from the pump sent strong vibrations through the boiler. I was impressed that such a small motor was causing such strong pulsing. Pressure readings from the digital pressure sensors on the boiler were reading around 200 psi.

When I reached 75% PWM, pressure was up to 450 psi. At this point, the motor was getting hot so I took a break to allow the motor time to cool.

Turned out, that was the last testing I've been able to do as the rains have moved in, and my test stand is outdoors,...now covered with a rain tarp.

I ordered a check valve a few days ago,..should arrive soon; hopefully it will reduce the pump induced pulsing in the boiler, if not, I may look for a different pump. I worry the pulsing will damage the copper tubing when the boiler is hot.

 

[Steamchick]

You are right. The gauge is probably reading "RMS" pressure, but the peak instantaneous pressure will damage the copper pipes.
You need a reservoir - a dead-end pressure vessel connected by a relatively small connection - may pipe ID ir reduced to half? - to contain some air that will act as a damper to the pulsations. Like a capacitor does on noisy power supplies. It acts the same way as a Helmholtz resonator - you can possibly tune it to your favoured frequency with some maths!
K2

 

[Toymaker]

I finally got around to taking a few pics of the current boiler plumping.
First up is the cordless Pressure Washer pump & motor.

Below shows input plumbing in foreground with the air blower for the burner in the background.

Below shows steam out plumbing from the boiler. Notice the same pressure and temperature sensors on the output as are seen on the input. This arrangement is used to test feed pump pressure.

 

[Toymaker]

You are right. The gauge is probably reading "RMS" pressure, but the peak instantaneous pressure will damage the copper pipes.
You need a reservoir - a dead-end pressure vessel connected by a relatively small connection - may pipe ID ir reduced to half? - to contain some air that will act as a damper to the pulsations. Like a capacitor does on noisy power supplies. It acts the same way as a Helmholtz resonator - you can possibly tune it to your favoured frequency with some maths!
K2

Yes, I'm familiar with reservoirs (aka accumulator), they're similar in function to the air pressure accumulator/oil separator I use on my swash plate air compressor for the venturi effect fuel nozzle. As you alluded to, I believe they work best when the in-out orifice is sized to smooth a fixed flow rate and pressure. My monotube boiler needs to work at wide range of both pressures and flow rates,....I'm skeptical tuning will be possible.

Troll suggested I use a check valve to capture the peaks and keep them in the boiler. I'll give that a try and see what happens.

 

[The Ignoble Troll]

Yes, I'm familiar with reservoirs (aka accumulator), they're similar in function to the air pressure accumulator/oil separator I use on my swash plate air compressor for the venturi effect fuel nozzle. As you alluded to, I believe they work best when the in-out orifice is sized to smooth a fixed flow rate and pressure. My monotube boiler needs to work at wide range of both pressures and flow rates,....I'm skeptical tuning will be possible.

Troll suggested I use a check valve to capture the peaks and keep them in the boiler. I'll give that a try and see what happens.

Sorry, to clarify, I meant using a check with a drain on the gauge to enable the actual top pressure reading, rather then a possible average aka RMS.


A check after the pump and before the coil, might smooth things out by providing drag, but it would not be optimal. The pump already has, likely, three down stream check valves.

While an accumulator might be out of the question, a simple coil of tube might do it. We removed pulsations in a manually cranked hydraulic set up by just throwing a roll of copper tube after the pump. The tube acted as a spring and worked great plus no parts to service. The longer the better and just use an hydraulic nomagraph to pick the diameter and thus constriction. If it doesn't work, you still have the tube essentially unaltered for other purposes.

 

[TimTaylor]

I finished plumbing in the tiny pressure washer pump and ran a few initial tests. I'm being very cautious because I don't want to burn out the tiny motor, which is rated for 18 vdc, and I'm giving it twice that (36 vdc) via a PWM (Pulse Width Modulation) motor driver. With the PWM set to 30% , I slowly closed the steam output valve to reduce the orifice size the pumped water was being forced thru, resulting in higher pressure from the pump. As pressure increased, motor RPM decreased and pressure pulses from the pump sent strong vibrations through the boiler. I was impressed that such a small motor was causing such strong pulsing. Pressure readings from the digital pressure sensors on the boiler were reading around 200 psi.

When I reached 75% PWM, pressure was up to 450 psi. At this point, the motor was getting hot so I took a break to allow the motor time to cool.

Turned out, that was the last testing I've been able to do as the rains have moved in, and my test stand is outdoors,...now covered with a rain tarp.

I ordered a check valve a few days ago,..should arrive soon; hopefully it will reduce the pump induced pulsing in the boiler, if not, I may look for a different pump. I worry the pulsing will damage the copper tubing when the boiler is hot.

Pressure washer pumps are positive displacement pumps and the pressure pulses you are seeing are a normal characteristic of their operation. The frequency of the vibration in CPM will be the number of pistons multiplied by the run speed of the pump motor, so it will vary with motor speed. Those vibrations can be destructive, especially if they excite a structural resonant frequency.

You'll never completely get rid of them, but as Steamchick suggested, a pulsation dampener downstream of the pump would definitely help level them out. Typically it's a larger diameter vertical pipe section with either some trapped air or a bladder in the top 1/3, which provides a compressible volume for the pulses of non-compressible water to work against and help average them out.

 

[Toymaker]

Sorry, to clarify, I meant using a check with a drain on the gauge to enable the actual top pressure reading, rather then a possible average aka RMS.


A check after the pump and before the coil, might smooth things out by providing drag, but it would not be optimal. The pump already has, likely, three down stream check valves.

While an accumulator might be out of the question, a simple coil of tube might do it. We removed pulsations in a manually cranked hydraulic set up by just throwing a roll of copper tube after the pump. The tube acted as a spring and worked great plus no parts to service. The longer the better and just use an hydraulic nomagraph to pick the diameter and thus constriction. If it doesn't work, you still have the tube essentially unaltered for other purposes.

Thanks for the clarification

I'm now seriously considering doing what I previously said I didn't want to do, that being to build a small hydraulic pump from scratch. I really don't want to take the time I know will be needed, likely several weeks to several months,...but I'm also extremely disappointed, (and surprised) by the strong pulsing vibrations generated by the tiny pressure washer pump; it really does rattle the entire boiler.

If I proceed with a DIY pump, I favor a swashplate axial design similar to this one I pulled off the web.

Cylinder block, Pistons, Port plate, Valve plate & Swash plate would all be brass due it's easy sliding, self lubricating properties. Metal housing & Retaining plate would both be aluminum.

A very important component which isn't shown in the above drawing is the coil spring which pushes downward against the Retaining plate and upwards against the Cylinder block. The spring pushes against the Retaining plate, thereby keeping the pistons in contact with the swash plate, while at the same time, pushing the Cylinder block against the Valve plate to form an effective seal. My question: how much force is needed to effectively seal the valve plate against the Port plate to prevent leaks? Are a few ounces enough? Or do I need many pounds of force?

 

[TimTaylor]

Thanks for the clarification

I'm now seriously considering doing what I previously said I didn't want to do, that being to build a small hydraulic pump from scratch. I really don't want to take the time I know will be needed, likely several weeks to several months,...but I'm also extremely disappointed, (and surprised) by the strong pulsing vibrations generated by the tiny pressure washer pump; it really does rattle the entire boiler.

If I proceed with a DIY pump, I favor a swashplate axial design similar to this one I pulled off the web.View attachment 156456

Cylinder block, Pistons, Port plate, Valve plate & Swash plate would all be brass due it's easy sliding, self lubricating properties. Metal housing & Retaining plate would both be aluminum.

A very important component which isn't shown in the above drawing is the coil spring which pushes downward against the Retaining plate and upwards against the Cylinder block. The spring pushes against the Retaining plate, thereby keeping the pistons in contact with the swash plate, while at the same time, pushing the Cylinder block against the Valve plate to form an effective seal. My question: how much force is needed to effectively seal the valve plate against the Port plate to prevent leaks? Are a few ounces enough? Or do I need many pounds of force?

This is still a positive displacement design and like the pressure washer pump, it will generate output pressure pulses. The frequency will be higher (CPM= # of cylinders multiplied by the motor RPM; frequency in HZ=CPM/60) because there are more cylinders, but they will still be there.

It would be a lot easier to build a pulsation dampener to be installed downstream of your existing pump. You could do it based on some off the shelf schedule 80 pipe fittings.

This is why most boilers use a high pressure multistage centrifugal feedwater pump - there is still a blade pass frequency generated, but the energy is lower by orders of magnitude.

 

[Toymaker]

This is still a positive displacement design and like the pressure washer pump, it will generate output pressure pulses. The frequency will be higher (CPM= # of cylinders multiplied by the motor RPM; frequency in HZ=CPM/60) because there are more cylinders, but they will still be there.

It would be a lot easier to build a pulsation dampener to be installed downstream of your existing pump. You could do it based on some off the shelf schedule 80 pipe fittings.

This is why most boilers use a high pressure multistage centrifugal feedwater pump - there is still a blade pass frequency generated, but the energy is lower by orders of magnitude.

The current pressure washer pump has a single piston which moves back and forth within a cylinder. Pressurized water is collected from both cylinder ends, effectively giving this pump two cylinders. The swashplate axial design would have 9 cylinders, with each cylinder pushing out slightly less than 1/4 the volume per cylinder, as compared to the current 2 cylinder pump, which should significantly reduce the "power" of each pulse, yes?

My analogy is this: each pressure pulse from the pump is like a hammer blow. A 2 cylinder pump is like having 2 very large hammers generating shock waves, while a 9 piston pump is like having 9 much smaller hammers generating lots of much smaller shock waves.

I'm also approaching this from my electronics background where I know that rectifying 400 Hz and smoothing the output to a clean DC level, is much, much easier than starting with 60 Hz. In other words, an accumulator on the output of a 9 piston pump should work much better than an accumulator on a 2 piston pump, yes - no ??

From what I've read on the web, 7 and 9 piston pumps are significantly smoother than the more common 3 piston pumps. Yes - no??

 

[The Ignoble Troll]

The current pressure washer pump has a single piston which moves back and forth within a cylinder. Pressurized water is collected from both cylinder ends, effectively giving this pump two cylinders. The swashplate axial design would have 9 cylinders, with each cylinder pushing out slightly less than 1/4 the volume per cylinder, as compared to the current 2 cylinder pump, which should significantly reduce the "power" of each pulse, yes?

My analogy is this: each pressure pulse from the pump is like a hammer blow. A 2 cylinder pump is like having 2 very large hammers generating shock waves, while a 9 piston pump is like having 9 much smaller hammers generating lots of much smaller shock waves.

I'm also approaching this from my electronics background where I know that rectifying 400 Hz and smoothing the output to a clean DC level, is much, much easier than starting with 60 Hz. In other words, an accumulator on the output of a 9 piston pump should work much better than an accumulator on a 2 piston pump, yes - no ??

From what I've read on the web, 7 and 9 piston pumps are significantly smoother than the more common 3 piston pumps. Yes - no??

100%

That's why most pressure washer pumps have three pistons, one always pushing.

The more the better.

Edit: pressure washers may also preload the unloader so the unloading valve is slightly open. This protects the valve by cushioning it and provides a little pulse dampening.