Hum/vibration in J&S 540 hydraulic system - Page 3
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  1. #41
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    Quote Originally Posted by Mark Rand View Post
    I've taken the marks on my one's level gauge to be the high and low level marks .
    Strange that the level tube has so much space above the upper line, isn't it?

    The fitting is a common or garden compression olive. if you can't get a replacement, you can turn one up from brass to the same approximate shape and it will work perfectly, The thread on the compression nut may be M13x1 on yours, but I would check to make sure that it isn't 1/2" x 26tpi (which is probably what it would have been in pre-metric days)
    It's not 1/2 x 25 TPI, the OD is 12.92mm (definitely more than 1/2" = 12.7mm) and there is enough thread to distinguish 25.4 TPI (1mm pitch) from 25 TPI. Conclusion: it's M13 x 1mm.

    What's the official or formal name for these "common" fittings? The people in my local hydraulic supply company didn't recognise it.

    As for the different hydraulic hose (or length of hose) absorbig the vibration, It makes me wonder if a small hydraulic accumulator might have the same effect?
    That's for water, not hydraulic fluid. Might work fine, but isn't "soft hose" simpler?
    Last edited by ballen; 08-10-2020 at 03:17 AM.

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    I think all of that type fittings are called - compression coupler/fitting, some use the ring to grab and hold the pipe and the pipe ID conforms to the fitting and makes the seal, in others, like hard copper piping, the ring itself is compressed and forms the seal

    regarding that accumulator, there are dampeners for hydraulics, some are made to specific pressures, some are adjustable, but "balloon" piping is definitely cheaper

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    Yeah, compression fitting. I'm surprised they haven't heard of it... Pretty common here in low to medium pressure hydraulics and air lines.

    The pressure thing is normal, when the hydraulic pressure isn't needed, the machine bypasses the hydraulic oil back to the sump. Most likely there's a switch on the table lever that controls a hydraulic solenoid to divert the flow. My Micromaster is the same, only about 25 psi when the table lever is in "off" position, about 120 psi when in "on" position. As I understand it, this is to keep the oil from heating up when the machine is idled.

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    We have plenty of compression fittings here. These have formal names/types/sizes, and are defined by standards, so that when different manufacturers make them, they are interchangeable/compatible.

    Did Jones and Shipman invented their own non-standard compression fitting? If not, what is the formal name or type?

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    is this the one you have? - https://uk.farnell.com/norgren/36050...5?ost=36050005

    I'd look for these at compressed air supplies

    edit: TDS on that page - http://www.farnell.com/datasheets/27479.pdf <- this, shows tools, dimensions and assembly instructions

    having seen all sorts of these in scientific lab equipment, some even have inch/metric threads on the same single piece fitting... tapered threads, straight threads, all sorts of pitches and sizes, I doubt there is a unifying standard for these, I guess tube/hose manufacturers just make stuff up to go along with their product

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    the breating of the hose makes it run smooth again
    That is the accumulating effect So that has to be kept

    Peter

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    Quote Originally Posted by jz79 View Post
    Thanks, that looks right. The shape and dimensions of the universal tubing sleeve on page N/AL 9.6.001.019 is the same as in my photo. So even though it appears to be a compressed air fitting, it's being used for low-pressure (7 bar) hydraulics.

    The catalog page describes these as "36 Series Metric". Do you know if there is a British or DIN or ISO standard for that series?"

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    no, I don't know of any standards for these, I'm not sure what you're looking to do there with that fitting, but IMO it would be easier to just make something that will fit, unless you need like 100 of them or more for some product line, it is metric after all...

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    Hi Peter,

    It's very rare that I don't agree with you, but here I think there might be more to it. You wrote:

    Quote Originally Posted by Peter from Holland View Post
    the breating of the hose makes it run smooth again. That is the accumulating effect So that has to be kept. 1
    The breathing is around 1 cycle/second ~ 1 Hz. But the "smooth running" is because it is absorbing noise from the gear pump at ~300 Hz. The hose that was recommended might be "stiff" at 1 Hz but still flexible (or even more flexible!) at 300 Hz.

    Cheers,
    Bruce

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    Quote Originally Posted by eKretz View Post
    The pressure thing is normal, when the hydraulic pressure isn't needed, the machine bypasses the hydraulic oil back to the sump.
    I think it's more complicated, because I am measuring the pressure just at the output of the pump. Do you think that the internal pump bypass valve is set for 2.5 bar or 6.8 bar?

    If the valve is set for 2.5 bar, then I should never measure a pressure higher than 2.5 bar. But I measure 6.8 bar in some conditions. So the bypass valve is set for 6.8 bar.

    If the bypass valve is set for 6.8 bar, then I would expect to measure 6.8 bar when the pump is not providing a lot of external flow (liters/minute) so the internal bypass valve is open, and a lower pressure when the pump is providing lots of external flow (so the internal bypass valve is shut).

    But it's the OPPOSITE: when the pump is providing no external flow, the output pressure is 2.5 bar. When the pump is providing high external flow, the output pressure is 6.8 bar!

    Most likely there's a switch on the table lever that controls a hydraulic solenoid to divert the flow.
    In certain table throttle positions, the flow is diverted away from the hydraulic cylinder. But it is NOT diverted away from the pump: it goes from the pump outlet, over the tubing to the top of the machine, and then back down to the pump inlet.

    My Micromaster is the same, only about 25 psi when the table lever is in "off" position, about 120 psi when in "on" position. As I understand it, this is to keep the oil from heating up when the machine is idled.
    This is the same as I observe in my machine. But for the reasons I give above, I don't understand it.

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    The bypass is not internal to the pump, it will be somewhere in the output piping. It is just a return line going back to the sump with a valve that's closed when the table throttle is in operating position and open when it's not. So when the bypass valve is closed (table throttle valve on), the full pump pressure set by the relief valve goes through the hydraulic system and it will hit 100+ psi. When it's open (table throttle valve off), the oil goes through the open valve and diverts back to the sump (effectively the same as the pump inlet) at a lower pressure. There is enough restriction in the piping and valve that some residual pressure still remains - these pumps flow a pretty good volume of fluid. I remember you posted a hydraulic circuit diagram somewhere... Did you look closely at it to see the flow directions? There must be sump returns either at a single whole-system bypass valve or perhaps each section has its own.

    So basically, when you think the pump is providing no flow, it actually is, just not to the hydraulics - only back to the sump. It's recirculating the oil at lower pressure. If the pump were dead-headed you'd find that it would overheat pretty rapidly. If your system just recirculates from outlet to inlet then that should work to drop the pressure just the same, but that loop would tend to heat up I'd think. On my machine it recirculates to the sump and sends all the sump oil through the recirculation to keep everything cool.

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    Quote Originally Posted by eKretz View Post
    The bypass is not internal to the pump, it will be somewhere in the output piping.
    That's not correct. The bypass/relief valve is internal to the pump. It is item 11 at the bottom of this schematic:



    To be more specific, the pump in the base of my machine has four main connections:

    (1) A filtered input at the bottom that sits in the sump
    (2) A pressure outlet at the top, going up to the saddle
    (3) A return line at the top, taking oil coming back down from the saddle
    (4) An outlet at the bottom, directing the oil from (3) back into the sump.

    The bypass valve (set to 6.8 bar) is internal to the pump. Inside the pump body, one side is connected to (2) and the other side is connected between (3) and (4).

    I am measuring the pressure at (2). This is 2.5 bar when the pump is not sending oil up to the saddle, and is 6.8 bar when the pump is sending the largest volume of oil up to the saddle. I don't understand that. I thought I would see high pressure when there is little oil coming from the pump, and lower pressure when there is more oil coming from the pump.

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    Nope. Bypass valve is not a relief valve. Totally different item. You don't seem to understand how the system works I think. You keep saying "when there is oil flowing from the pump" and "when there is no oil flowing from the pump." In a hydraulic system, if the pump motor is running, there is always oil flowing from the pump. It is either being bypassed back to the sump or directed through a cylinder to move the machine. There's no way to magically shut off the oil flow from the pump at will. The pump rotors/gears are directly driven by the motor. There is some sort of bypass and return to the sump somewhere. In your circuit diagram have a look at the lower left with the check valve... That may be it. Also notice the valve there has an outlet that looks like it goes into an upside down "T" - that's a return to the oil reservoir. There are a bunch of those in your diagram. I didn't take the time to study it closely but there are clearly return lines to the sump. They may be routed in a way that's not clearly visible. They may all route back into that one return line.

    Anyway, the pressure decrease is completely normal, and the reason why is described in my previous post.

    Looking at the manual for my machine, it's noted that when the table valve is in the off position, the lines for the cylinder are connected to each other, allowing oil to flow freely back to the sump... Your machine may be similar.

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    Had a minute to look a little closer and yep, looks like your grinder does connect the cylinder lines together when the throttle valve is in neutral or off position. So there's your bypass back to the sump.

    20200810_095521.jpg

    20200810_100132.jpg

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    Quote Originally Posted by ballen View Post
    Hi Peter,

    It's very rare that I don't agree with you, but here I think there might be more to it. You wrote:



    The breathing is around 1 cycle/second ~ 1 Hz. But the "smooth running" is because it is absorbing noise from the gear pump at ~300 Hz. The hose that was recommended might be "stiff" at 1 Hz but still flexible (or even more flexible!) at 300 Hz.

    Cheers,
    Bruce
    I imagened the frequency of breating was simultanisly with the movement of the table
    Isn`t that the case ??
    For some reason I thought to remember the hum was only at the end of stroke But I mix up 2 of your posts I think
    If the hum is always present my idea would be that those hoses are too small so the speed of the oil is too high and therefore noisy The noise is not present at lower speed you say
    Any hose with bigger ID would do IMHO But for J&S to do that nicely they need bigger fittings So they opted for a "dampening hose"

    Peter

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    Quote Originally Posted by eKretz View Post
    Had a minute to look a little closer and yep, looks like your grinder does connect the cylinder lines together when the throttle valve is in neutral or off position. So there's your bypass back to the sump.
    I agree with the path that you've drawn. But it illustrates exactly the thing I am confused about. To help explain, I've redrawn it here:



    This shows the path followed by the oil, as it leaves the pump, passes through the variable throttle control valve V, "through" the cylinder, and back down past the bypass valve and into the sump. Note that the pressure relief valve (green path) will open if the pressure between point a and point b is more than 6.8 bar, and will otherwise close.

    Consider two possible settings of the throttle valve V:

    (1) When V is almost closed (table moving very slowly) there is very little oil passing upwards past the point a and very little oil passing downwards past the point b. So I would expect that the bypass valve (green path) is open, and the pressure at point a is 6.8 bar. However in this case (throttle valve V almost shut) the pressure at point a is 2.5 bar.

    (2) When V is almost open I would expect that lots of oil passes by point a and by point b. Since the pump output is not restricted, the pump can not develop a lot of pressure. So in this case the bypass valve should be closed, and the pressure at point a should be much less than 6.8 bar. However in this case (throttle valve V wide open) the pressure at point a is 6.8 bar!

    Please note that there is no return path to the sump which does NOT pass by the relief valve. The red path at b is connected directly to one side of the relief valve (green path).

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    Yes there is a return path outside the relief circuit...According to the circuit diagram your line 'b' is connected to the outlet side of the relief valve... It doesn't pass through the relief valve. The system restriction with this routing is low enough that the oil can't develop any more pressure than that 2.5'ish bar, so the relief valve doesn't enter the equation. Once the throttle is turned on one of the other valves in the system will lock out that flow so that the oil is kept out of the bypass and rises to the pressure set at the relief valve. I'm sure the pump is certainly plenty capable of keeping up 6.8 bar at full flow. If your machine is only hitting 2.5 bar with the table moving perhaps you have a sticky valve. Mine jumps to the high relief pressure as soon as the throttle is moved out of the off position.

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    Bruce's pressure is rising after the throttle is turned on, as you and others have explained. That's what was confusing him. Gear pumps are a bit like an unstoppable force.
    Last edited by Mark Rand; 08-11-2020 at 03:45 PM. Reason: Spelt Bruce's name wrong!

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    I've understood what is happening now. It's the following (referring to the diagram):



    (A) When the throttle valve is off, normally there would be high pressure in the hydraulic system, since throttle valve off blocks the flow. However when the valve (4 in the diagram) is in the off position, the top block (of the three shown in the diagram) is engaged. This connects the pump output to both ports of the hydraulic system and to the return line. So with the throttle valve off, the pump flow is unrestricted and the pressure is 2.5 bar.

    (B) When the throttle valve is moved to the mid-off position, it engages the bottom block shown on valve 4 in the diagram. This now cuts the flow from the pump, and the pressure is then 6.8 bar as set by the relief valve.

    (C) When the throttle valve is in the fully on position, the flow would normally be restricted by the cylinder, leading to relatively high pressure (say 6 bar). However I have been measuring the pressure with the table feed turned off. When the table feed is turned off (via the cycle start valve 7) this engages the trip valve 6, which moves the main reverse valve 2 to the center position. In the center position, both ports of the hydraulic cylinder and the line feeding them are connected to the return path to the pump. So the hydraulic pressure is low (2.5 bar).

    (D) If I engage the table feed with the throttle valve in high, or I flip the table reverse valve (3) which then pushes the main reverse valve (2) off center, this cuts off the flow on the return path to the pump, and the pressure goes high again (say 6 bar).


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