Piston Pumps (Full Lecture) 

I don't have a lot of experience with jet turbines, however, I do know that some mobile (ie: forklifts, etc) use a pressurized reservoir rather than atmospheric/vented reservoir.

Honestly best place to get this data is directly from the pump manufacturer for the pump of interest. Often they'll have applications engineers on staff that can guide you through these very specific applications. Pumps in parallel need to be very similarly rated. With perfectly matched pumps in theory you'd double flow at a specific load induced pressure ... however ... with twice the flow one might observe increased pressure drop across components and valves.

@@bigbadtech thanks mate. I had been trying to avoid the manufacturer. Ive utilised all there technical docs on the website which are indeed super detailed. Ill reach out to danfoss. Thanks again

Hard to answer without drawing a diagram so hopefully this description will help. FWD: Flat plate = no flow, left side up, right side down = full flow forward REV: Flat plate = no flow, left side down, right side up = full flow forward Not sure if you'd want to do this though because the P and T pipe diameters are typically different diameters.

+John C I'm out of my league when it comes to the specifics of mobile hydraulic applications, however, this might be an example of something called a "constant horsepower" pumping circuit. I have another general pumping circuits lecture in the works detailing pressure compensated and load sensing configurations as well as a brief primer on constant horsepower applications. Long story short ... you're absolutely correct. If the product of torque and rotational speed (plus a constant accounting for unit conversions) equals mechanical power, if speed goes down, torque goes up, keeping mechanical power constant.

+John C If you refer to 14:09 in the video during the pump data sheet explanations; you can find the answer; or at least provide some aid to the answer you seek I believe. Here is the citation of Jim Pytel at that mentioned reference point- “ As we’d expect; flow rate goes down, at higher pressures, given increased leakage, and the tendency of the nominal rotational speed of the prime mover to decrease given higher torque requirements at higher pressures. “ To express my humble opinion, and finding based on my experience with such type of machines you are referring to- A high flow rate indicates less induced pressure resistance created by the load the machine is transporting, which conveys the idea of less torque power requirement. In contrast, a lower operational flow rate of the pump indicates increased pressure resistance created by the load the machine is transporting; which conveys the idea of higher torque power requirements. Essentially for the machine to operate at the given high flow rate you mentioned, the pump and motor is incapable of providing the required torque power to transport the given load. Additional to that; I’m not sure if the machines you are referring to has this option; the machine brand I am familiar with have a high flow option. What that means is when this option is selected; for a given oil quantity provided by the pump to actuated the motor; half the allocated motor input is used. Additional surplus pressure is relieved by a pressure relief valve. This would mean the inrush of pressurized oil to the motor is confined to half of the allocated space; reducing the speed of the machine while increasing its torque and power. This would conclude and provide the answer to your query; if the machine you are referring to has this option. I hope that makes some sense. Cheers mate!

In my humble experience with caterpillar hydraulic systems ,we have to remember that there's certain amount of pressure check valve's and electric-hydraulic sensors (newer machines) that protects the pumps against back pressures (due to flows laws),soo certain behaviors of the hydraulic system at pushed throttle or high levers speed? ends in that !!!

Think of it like a hydraulic jack. If your pump is at min swash and your hydrostatic motor is at max swash you have effevtively gained a reduction.

May i know any information further/link related to dual piston pump. Thanks in advanced!

+D. G. As with everything ... money! Fixed displacement pumps are simple and inexpensive however flow is constant if the primer mover is fixed speed. Variable displacement pumps are more mechanically complex however flow can be varied.

Tx Mr. Pytel, Could one assume that cranes,front end loaders etc use a fixed pump for mobil operations?

+D. G.I believe I can provide an answer to that question; as I'm familiar with the hydraulics / hydrostatic systems to mobile construction equipment specifically compact Skid Steer Loaders. Before I attempt to answer the question; I must say, hats down, I am an avid fan of Jim Pytel’s merited exemplary lectures; that frames the topics discussed comprehensibly and non-intimidating. From what I’ve been across with in mobile construction equipment the hydrostatic (term for hydraulic fluid drive power) system consists of a variable displacement pump and a motor. The variable displacement pump’s job is to actuate the motor, which in turn rotates the wheel to drive the Skid Steer Loader machine. The pump is intentionally a variable displacement pump; specifically a variable displacement axial piston pump. As one would expect the drive system needs to be setup in a way that is able to be precisely controlled and managed by the operator in the machine. A fixed displacement pump in this type of application would not be practical at all as one would imagine after understanding the concept differences between variable displacement pumps and fixed displacement pumps. The person operating the machine can adjust the drive speed by adjusting the angle of the axial piston pump’s swash plate; either by manual actuation from a pedal that has a mechanical linkage to the swash plate, or electrical actuation through joystick operation that energizes a three position, four way, spring centered, double solenoid, solenoid operated valve. As you can imagine the machine can drive forward and reverse, thus the reason for the double acting solenoid valve unit. Each solenoid is assigned for one swash plate angle side. One angle side of the swash plate drives the machine forward, and the other side of the swash plate angle drives the machine in reverse. I’ll discuss this in more details once I’ll reach the hydrostatic axial piston pump in the video series I started performing each week on Saturday; with the systems and applications being discussed belonging to a Skid Steer Loader Machine. I’m particularly fond of Skid Steer Loader machines because in my humble opinion; they imply and encapsulate all the major hydraulic components; and is a great way to learn about hydraulic systems and its constituent components; without being horrifically complicated as some other machines like the Telescopic Machine. I hope that helped.. Cheers mate.

@@northernfreedom6252 thanks for sharing 😊

With closed center valve pressure will rise to setting of pressure relief valve at which point pressure relief valve will open and spill flow to tank

@@bigbadtech But pressure has not shown in relief valve's gauge .. After reaching the cracking pressure then pressure relief valve activate..i actually want know in unloading condition how pump drain the oil?

Check out the "Hydraulic Pumps" lecture at: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-TBxMgGq3O94.html I discuss load sensing pumps in general terms in this lecture. In the unloaded condition a variable displacement pump "destrokes" to a very small displacement per revolution. Any leakage is channeled away via the variable displacement pump's case drain.

Here's a link to the online collection of study guides for hydraulics. Feel free to print. openoregon.pressbooks.pub/hydraulics/

أنا لا أتحدث الإنجليزية جيدًا

@@bigbadtech I am also not good at English. If you add the Arabic language in the translation, you will get many views. The Arabic content on RU-vid is weak like this. Thank you for the great content.