Omax / Maxiem Waterjet Retrofit
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  1. #1
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    Default Omax / Maxiem Waterjet Retrofit

    I figured I would start a thread on my experience with Omax/Maxiem. This is in no way an endorsement for or against any particular manufacturer. Just my experience and opinion.

    Right now my company is in the process of replacing the original (2) 40hp Omax/Maxiem direct drive pumps with a single H2Ojet intensifier style pump. Admittedly our use of the waterjet is not traditional as we are utilizing water-only technology for cutting plastics. Not cutting out parts, but creating slots or openings by the stream diameter

    While traditional abrasive cutting is what most people are employing, some of the issues or problems I've encountered may not be applicable to you.

    Direct drive - The pump utilizes a 3 cylinder, piston, and head/manifold design to manufacture/create the high pressure stream of water. Most do not employ an attenuater to equalize pressure and rely on 2 valves to to distribute pressure through the cutting head or through a pressure relief or dump valve.
    This system, I have found, has some major inequities in properly maintaining a constant pressure, which results in premature failure of valves, fittings, and tubing. It also has an effect on cutting results.
    After a year of changing out and replacing these components, a rep suggested I install a pressure gauge inline to see what was going on. Most waterjet manufacturers, I notice, include a high pressure gauge as an option or demo a machine with one installed. Omax/Maxiem does not. I guess I found the reason.
    A few minutes of operation and documenting pressures, I was recording an amazing +/-20ksi variance in line pressure. The fitting and tube was seeing extreme pressure swings. With some fine adjustment we were able to get it down to +/-10ksi variance, but that is still a 20ksi swing in pressure. Note that setting and calibrating through the pump and Omax/Maxiems specifications and readings for a 3ksi variance of on/off cycle, water/pump only.
    In other words, there was a major difference in pump reading of pressure and actual in line pressure.
    At 30-40ksi and abrasive additive cutting of metals and granite this may be different, but at 42-50ksi, it is horrible and expensive for maintenance.

    We just poured the slab for the waterjet's new location and should be installing water table and H2Ojet pump in their new respective locations in the next two weeks. Tech is scheduled for 1st week of October. I'll post some pics as it unfolds. Definitely some none typical utilization such as direct drain table, i.e. no residual water in the tank, as well, as some water reclaim that is application specific.Spoiler - I can't show specifically what we are cutting.

    *If anyone is interested in (2) Omax/Maxiem 40hp direct drive pumps, let me know. I'll be contacting machine dealers in the near future. Both pumps have less than 100hrs. since their last rebuild. Also have some spare parts that go go with.

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    Good to see your putting some methodology into this.

    Hydro-pac in Fairview IIRC makes the hydraulic intensifier
    waterjet pumps.

    as far as not showing us the product, that's o.k., one of the things cut with them is dead fish....ugh

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    The nature of any crank driven pump is pulsation, the pistons are constantly accelerating or decelerating and thats changing your flow rate at any given moment, pumping compressible gases no issue, pumping minimally compressible liquids especially through a fixed orifice its hardly surprising your going to get pulsation. IMHO should have been as simple a fix as adding a accumulator tank to the system, though that's probably a pretty expensive fitting at these pressures.

    Its kinda the fundamental reason that all hydrulic pumps don't use cranks, there either a gear pump or a axial swash plate setup. Neither pulsate - they both deliver a near constant flow rate at any point in there respective rotation.

    Whilst i grasp not showing us the product, enquiring minds do wonder how you deal with the pierce hole? Or with just water is this not much different to the slot?

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    I own an OMAX 55100 tilt-a-jet with a 40HP piston pump and have been thinking the same thing, but haven't taken the time to put a pressure sensor on the oscilloscope to see what is really going on. When I cut thinner materials, say 0.063" aluminum or stainless where the machine ends up moving along pretty quickly even at higher quality settings, I notice periodic variations in the kerf which seem likely to match up with pulsations in the pump. It does seem like even a small pressure accumulator could smooth things out quite a bit, although for safety you would want to make sure that the system always gets depressurized through the dump valve after use.

    I guess another possibility is that the valves on each of my pump cylinders or one of the pistons is not performing the same as others which could be creating additional pulsation at the crank frequency instead of only at 3x the crank frequency.

    Anyone else see this problem?

    Quote Originally Posted by adama View Post
    The nature of any crank driven pump is pulsation, the pistons are constantly accelerating or decelerating and thats changing your flow rate at any given moment, pumping compressible gases no issue, pumping minimally compressible liquids especially through a fixed orifice its hardly surprising your going to get pulsation. IMHO should have been as simple a fix as adding a accumulator tank to the system, though that's probably a pretty expensive fitting at these pressures.

    Its kinda the fundamental reason that all hydrulic pumps don't use cranks, there either a gear pump or a axial swash plate setup. Neither pulsate - they both deliver a near constant flow rate at any point in there respective rotation.

    Whilst i grasp not showing us the product, enquiring minds do wonder how you deal with the pierce hole? Or with just water is this not much different to the slot?

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    Long time OMAX Maxiem owner. I think the direct drive pumps are a good thing.

    All OMAX/Maxiem direct drive pumps already have snubbers, to minimize pulsation. The snubber is a short straight fitting, male one side, female other side, with an orifice sized for the normal operating flow+pressure for your pump and nozzle configuration. It's typically screwed into an elbow and easy to overlook. Or maybe someone removed it. If you are cutting a lower than normal pressure, tell OMAX what you're doing and ask for the correct snubber for your configuration. To be clear, it's an attenuator, not an accumulator.

    OMAX does offer an instantaneous direct reading high pressure transducer, that screws into a tee fitting. They're not cheap. My machine has one. Ordinarily it feeds an analog signal into the pump VFD, which scales it to display PSI. (Without the transducer option, the VFD displays system PSI based on scaling the motor torque. That's accurate within a few percent but does not show spikes.)

    The VFD samples and updates the display only a couple times a second and so the VFD readout has to be sampled to determine the range of short duration spikes. The OMAX software includes a sample routine to do that, cycling the nozzle in a pattern where you watch the VFD display for a minute and will eventually see the spike range. In a normally adjusted range it's 2 to 3K.

    You can, and this is routinely done when you have a reason to, connect the pressure transducer to an oscilloscope or a peak-reading DVM, and see spikes more precisely.

    A high rate of on/off cycles with a larger pressure spread will blow up your plumbing in a month. Spikes of 20K, that's not normal, that indicates a gross problem in your system completely unrelated to the design. Most likely one or both the on/off and dump valve actuators have failed, & need the piston o-rings replaced, or better replaced with improved no-maintenance actuators they started offering a few years ago. Or perhaps someone messed with the air plumbing, and missed the manual warnings about keeping the nozzle and dump lines matched to ensure the actuators cycle in sync, with minimum spikes.

    OMAX offers other options to reduce fatigue effects for folks doing high-cycle cutting. Ask them.

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    A accumulator to take out these pulses would not prove that much of a danger, you don't need to store liters, just a 1/5th or so of one of the pumps swept cylinder volume should be ample to get rid of the pulsation, but again why are they not just using std hydraulic practice of swash plate style pumps and not have any pulsation issues to deal with.

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    Quote Originally Posted by adama View Post
    A accumulator to take out these pulses would not prove that much of a danger, you don't need to store liters, just a 1/5th or so of one of the pumps swept cylinder volume should be ample to get rid of the pulsation, but again why are they not just using std hydraulic practice of swash plate style pumps and not have any pulsation issues to deal with.
    Are there examples of swash plate style pumps working at 50ksi+? I would have to think they considered some of these things before deciding to go the piston pump route. Perhaps it's a lubrication and sealing issue, since this is water and not hydraulic fluid.

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    The OP describes a special application, we don't know what considerations may be different from everyday abrasive waterjet cutting.

    IMO ripple from direct drive pumps is a red herring. Visible ridges in cut edges of thick material is more about turbulence in the jet and abrasive flow. The individual cylinder displacement is < .1 cubic inches, the equivalent of a few inches of high pressure pipe. That's maybe 1% of the volume of the piping between the pump and nozzle. At 50,000 psi water is compressible and has physical characteristics of both a liquid and gas. There isn't much trace of the ripple by the time the water passes the snubber, and less when it reaches the nozzle.

    Pressure spikes on the other hand are a big deal and are a problem for customers of all the manufacturers. Intensifier pumps don't eliminate spikes, on the other hand as I understand it they pretty much guarantee a moderate spike, maybe more than a properly adjusted direct drive, but the simplicity of the intensifier does limit how severe a spike can get.

    With the direct drive systems, the pump is fixed displacement, when the nozzle shuts a dump valve opens in sync, with fussy pneumatics to minimize spikes during the transition. For systems with multiple pumps and/or multiple nozzles, there can be some complexity to the pump, nozzle and software configuration to ensure the valves always open in proper coordination to maintain constant pressure.

    Again with the OP reporting measured spikes of 20Ksi, my experience is that just indicates something is wrong with their specific configuration. It's not a fundamental problem with direct drive pumps.

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    axial piston pumps do also pulsate.
    gear pumps leak far to much.
    accumulators need a way to keep the gas separate from the fluid. either a bladder or a piston. Those wear out. the volume has to be significantly larger than the amount of attenuation.

    If it were easy they would not cost so damn much.

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    Once you get over 4 pistons axial piston pumps won't pulsate, the pistons are all runing up a constant slope, ergo there all squirting out exactly the same qty of fluid at the same velocity constantly, unlike the varying velocity of pistons driven by a crank.

    I never said a accumulator would not have - be a wear issue, personally i don't know of much in the hydraulic world running above 300bar that’s not got wear issues. Yes there volume has to be bigger but at the flow rates and swept pump volumes were looking at here very very little is needed.

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    why not go for a KMT pump system, they have a attenuator in the system.

    Still it requires regular maintenance as valves ( outlet ), seals ( main piston) go every few months. Inlet valves seem to last a lot longer.
    There is a slight drop in pressure on cycle but not enough to effect cutting kerf, usually if kerf has a problem the diamond orifice is worn out, it will give a wavy appearance when this happens.

    check them out do a simple web search to find KMT.

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    Quote Originally Posted by adama View Post
    The nature of any crank driven pump is pulsation, the pistons are constantly accelerating or decelerating and thats changing your flow rate at any given moment, pumping compressible gases no issue, pumping minimally compressible liquids especially through a fixed orifice its hardly surprising your going to get pulsation. IMHO should have been as simple a fix as adding a accumulator tank to the system, though that's probably a pretty expensive fitting at these pressures.

    Its kinda the fundamental reason that all hydrulic pumps don't use cranks, there either a gear pump or a axial swash plate setup. Neither pulsate - they both deliver a near constant flow rate at any point in there respective rotation.

    Whilst i grasp not showing us the product, enquiring minds do wonder how you deal with the pierce hole? Or with just water is this not much different to the slot?
    Omax/Maxiem has an accumulator on their higher range pumps. It is the fluctuation on in line pressure pressure with air vs. electronic between the direct drive and intensifier style systems. With Omax/Maxiem pierce is controlled through both air actuation and parameters in application. Air pressure feeding system also plays a part especially when you are using multiple cutting heads. There is a calibration program help set the system up.

    The first thing I noticed once we got the new pump installed is that while increasing the speed/ipm with a slightly higher pressure of 58-60ksi, is that the bulk of time is spent on actuating the state and stop. going from 70ipm to 100ipm only shave about 4 minutes off total run time on a 9.75" x 48" section.

    Quote Originally Posted by Toolbert View Post
    Long time OMAX Maxiem owner. I think the direct drive pumps are a good thing.

    All OMAX/Maxiem direct drive pumps already have snubbers, to minimize pulsation. The snubber is a short straight fitting, male one side, female other side, with an orifice sized for the normal operating flow+pressure for your pump and nozzle configuration. It's typically screwed into an elbow and easy to overlook. Or maybe someone removed it. If you are cutting a lower than normal pressure, tell OMAX what you're doing and ask for the correct snubber for your configuration. To be clear, it's an attenuator, not an accumulator.

    OMAX does offer an instantaneous direct reading high pressure transducer, that screws into a tee fitting. They're not cheap. My machine has one. Ordinarily it feeds an analog signal into the pump VFD, which scales it to display PSI. (Without the transducer option, the VFD displays system PSI based on scaling the motor torque. That's accurate within a few percent but does not show spikes.)

    The VFD samples and updates the display only a couple times a second and so the VFD readout has to be sampled to determine the range of short duration spikes. The OMAX software includes a sample routine to do that, cycling the nozzle in a pattern where you watch the VFD display for a minute and will eventually see the spike range. In a normally adjusted range it's 2 to 3K.

    You can, and this is routinely done when you have a reason to, connect the pressure transducer to an oscilloscope or a peak-reading DVM, and see spikes more precisely.

    A high rate of on/off cycles with a larger pressure spread will blow up your plumbing in a month. Spikes of 20K, that's not normal, that indicates a gross problem in your system completely unrelated to the design. Most likely one or both the on/off and dump valve actuators have failed, & need the piston o-rings replaced, or better replaced with improved no-maintenance actuators they started offering a few years ago. Or perhaps someone messed with the air plumbing, and missed the manual warnings about keeping the nozzle and dump lines matched to ensure the actuators cycle in sync, with minimum spikes.

    OMAX offers other options to reduce fatigue effects for folks doing high-cycle cutting. Ask them.
    Sorry, this is something inherent in their system that isnt seen with conventional use. When you are placing thousands of 1.5" slots spaced .25" apart on long pieces of pvc, it is quite a bit different than cutting metal shapes. Also running at 45-50ksi continually warps the manifold and it needs replaced at each rebuild. We tested with the guage after installing the pressure control upgrade 2 years ago and through multiple rebuilds. It isnt an anomoly. The H2ojet rep suggested putting the guage in line and already knew of the issue. they have studied the omax pump system for some time and already aware of the problem.

    Quote Originally Posted by Toolbert View Post
    The OP describes a special application, we don't know what considerations may be different from everyday abrasive waterjet cutting.

    IMO ripple from direct drive pumps is a red herring. Visible ridges in cut edges of thick material is more about turbulence in the jet and abrasive flow. The individual cylinder displacement is < .1 cubic inches, the equivalent of a few inches of high pressure pipe. That's maybe 1% of the volume of the piping between the pump and nozzle. At 50,000 psi water is compressible and has physical characteristics of both a liquid and gas. There isn't much trace of the ripple by the time the water passes the snubber, and less when it reaches the nozzle.

    Pressure spikes on the other hand are a big deal and are a problem for customers of all the manufacturers. Intensifier pumps don't eliminate spikes, on the other hand as I understand it they pretty much guarantee a moderate spike, maybe more than a properly adjusted direct drive, but the simplicity of the intensifier does limit how severe a spike can get.

    With the direct drive systems, the pump is fixed displacement, when the nozzle shuts a dump valve opens in sync, with fussy pneumatics to minimize spikes during the transition. For systems with multiple pumps and/or multiple nozzles, there can be some complexity to the pump, nozzle and software configuration to ensure the valves always open in proper coordination to maintain constant pressure.

    Again with the OP reporting measured spikes of 20Ksi, my experience is that just indicates something is wrong with their specific configuration. It's not a fundamental problem with direct drive pumps.
    Exactly why we went with a intensifier system. They don't utilize a dump valve. It will still cycle electronically and through a pressure relief valve. They also recommended to have a gauge in line to help trouble shoot or see when a component is starting to fail and be proactive in maintenance, whereas the omax/maxiem tech played down the need for a gauge. Do you have a gauge inn line? Have you tested this? Or just having a theoretical conversation?

    Quote Originally Posted by Street View Post
    why not go for a KMT pump system, they have a attenuator in the system.

    Still it requires regular maintenance as valves ( outlet ), seals ( main piston) go every few months. Inlet valves seem to last a lot longer.
    There is a slight drop in pressure on cycle but not enough to effect cutting kerf, usually if kerf has a problem the diamond orifice is worn out, it will give a wavy appearance when this happens.

    check them out do a simple web search to find KMT.
    We have the system set up and really required less than i thought. Pretty simple. Unfortunately have dot had much time on r=d after it was installed due to other more pressing priorities( flying to Charlotte this week / in hydraulic test facility last week).

    Will be looking to optimize the pierce process when i do get on to it. Unfortunately I need to get the code from omax. For some reason they pass-lock the settings to alter this function. Don't get me wrong, i really like the omax software and table. My only complaint is the amount of fat hanging off. $50k for a pump and $100k for the table. if you work in welding or fab and have a understanding of the motion control components, you get what i mean. That is actually the next thing i see. Independent manufacturers of table and control systems. Pick your pump, pick your table, and pick your application for control. Could shave more than $25k off the cost of a major manufacturer system with better components that could be cross applied for waterjet, laser, router, slitting, ect., ect.

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    Quote Originally Posted by Rodm1 View Post

    Exactly why we went with a intensifier system. They don't utilize a dump valve. It will still cycle electronically and through a pressure relief valve. They also recommended to have a gauge in line to help trouble shoot or see when a component is starting to fail and be proactive in maintenance, whereas the omax/maxiem tech played down the need for a gauge. Do you have a gauge inn line? Have you tested this? Or just having a theoretical conversation?
    Yes there's a honeywell high pressure transducer plumbed into a tee after the snubber. It's wired into an A-to-D input on the pump VFD and displays PSI on the VFD readout which is remotely mounted at eye level in front of the operator. It only samples a couple times a second and so does not directly display the extent of spikes, but it is a big help in keeping an instant eye on the overall health of the pump and plumbing. The transducer itself accurately reflects spikes - on occasion when I suspect spike and fatigue issues, I connect the transducer to an oscilloscope.

    I've had some experience with fatigue, as the nature of our business in the early years involved a lot of art glass, plastic and thin sheet metal cutting - high cycle rates, and low pressure pierces. I got as good a lesson as anyone in the impact of high cycle low pressure pierces on fatigue failures. I've learned a lot about how to mitigate that, with generous help from OMAX, and much figured out on my own. I don't know that it's right, it's just what has worked for us.

    Our machine has about 700,000 jet on/off cycles. That'd be high for someone cutting plate; it's low compared to some customers. In the first year, 2010, when we did tens of thousands of low pressure pierce / high pressure cut cycles, I didn't pay attention to fatigue issues, we blew up pretty much the entire machine worth of high pressure plumbing. Yet operating differently, since 2012, we've had pretty much zero fatigue failures - issues only with the valves and whips.

    What I observed is pressure cycling of 20Ksi or more for LP pierce / HP cut is death to the plumbing. For high cycle jobs that require LP pierce, we just dial the HP setting down to anywhere from 20K to 35K and run at constant pressure - HP pierce and cut as far as the machine thinks, except it's all at lower pressure. Most of the glass and plastic we cut works well with reasonable chipping at a straight HP pierce/cut at 30 to 35K. The 20K is for a trademark thing we do with finely controlled etching with super low abrasive feed (.1 lb/m). Regular metal cutting at 45K to 50K. Typically leave it 45K, a tradeoff to make it easier to mix in high-cycle jobs, the occasional part with 1000 holes, without thinking about it.

    Doesn't seem to matter how many tens of thousands of on/off cycles so long as the pump pressure is constant, the nozzle and dump valves are balanced and the valve actuators are in good condition.

    Regarding the manifold. I perceive the manifold and everything else under high pressure is affected by pressure spikes.

    We did the usual minor & major pump rebuilds for several years. Once we got in a groove keeping spikes under control, at 2400 hours we did a full overhaul with check valves, the manifold, port adapters, and then subsequently put an additional 3300 hours on the pump without touching the wet end. Even though you're supposed to renew the dynamic seals at 250 hours and overhaul at 2000 hours, we did nothing. The dynamic seals and the manifold leaked, but the pump worked fine, we just ran it until I felt it was time, and then bought a new wet end assembly (for $9000) and chucked everything. That isn't everyone's experience and I don't know it'll be ours again. 700 hours so far. Official recommendation is to service at 250 hour intervals (I only know about the standard pump) but unofficial is to run til it drops.

    My personal observation is water quality and pressure spikes are the biggest factors in the life of a direct drive pump.

    Your situation is different enough, I won't further speculate on what's right for you.

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    I'd love to know more about that low abrasive feed etching technique!


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    This is a bit of an aside, but this is by far the richest OMAX discussion thread I have seen in some time. I have always wondered why there isn't a more active OMAX discussion forum somewhere. I get that many people have production shops and feel that their accumulated knowledge is a competitive advantage over others, but compared to other machinery I have, waterjet discussion forums topics seem to be extremely quiet.

    OMAX seems to give good support to their customers, but I almost feel like they don't want their customers talking to each other. I'm basing that on the fact that they don't host any customer forum on their website.

    My personal experience in other domains is that forums tend to elevate everyone's knowledge and also alleviate the support burden of OEM.

    Thoughts?

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    I run a flow, but I agree with your assessment that online forums are pretty quiet on the subject. I hadn't been in here for a few weeks until Tuesday night, and was pleasantly surprised to see several water jet related threads.


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