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PHENOMENON OF PRESSURE ON THE MULTIPLICATION OF DIFFERENT LES CYLINDERS.

PHENOMENON OF THE MULTIPLICATION OF PRESSURE IN THE DIFFERENTIAL CYLINDERS.

One drawback when it regulates the flow at the exit of a differential cylinder.

time ago we attended a recurring failure that was presented in a hydraulic machine, this team, whose purpose is to place packages on a scale rods, consists of six identical differential hydraulic cylinders mechanically coupled in parallel with a levers, which are responsible for raising the packages to be placed on the scale. These cylinders are connected to a hydraulic whose pressure is 150 Bar (15 MPa). The operating speed of these cylinders is obtained by a unidirectional flow throttle valve positioned to regulate the flow of oil out of cylinders, has this is known as "regulation of the discharge." Because the loading conditions of flow control must be performed at discharge.

The flaw in question is untimely rupture of a hose next to the stem. While the hose attached to the cylinder piston side lasted years, stem side had an average life of just under one year of continuous service (24 hours a day). Like all fails, it usually occurs in the most inopportune times to other process of generating a surprising loss of hydraulic oil in a few seconds. Fluid spills came to reach almost 5,000 liters while the system is triggered by low oil and hydraulic accumulators are discharged from the facility.

hoses recommended by the manufacturer corresponding to SAE 100 R2 with a nominal diameter of one inch (1 "), which at first glance are suitable for pressure values \u200b\u200brecorded in the central power.

Why always side hose bursts stem?, Why the piston side lasted if both hoses are installed on the same cylinder at the same plant?. A short analysis of what happens in a cylinder differential regulation in the download explains the root of the problem while while giving us the solution leaves the intrigue of how a manufacturer of hydraulic machines make a mistake own selection of a beginner.

To understand what happens we have to understand some phenomena present in the hydraulic differential cylinders. The differential hydraulic cylinders are characterized by different effective areas between the piston and rod side of the annular area.

This difference in these areas makes hydraulic cylinder forces the piston side are greater than the rod side, the flows are uneven consumed or discharged one side over the other if you keep the speed as input and output, and finally can be operated as pressure boosters.

If we imagine the cylinder with the piston in its middle position, filled with oil and the output shaft side is closed, the pressurizing piston side, the stem shows a side product of the compression pressure of the fluid confined to this side . The hydraulic power source that is generated by pressure on the piston is set to the multiplication product of pressure by the same area. This force is applied in the fluid in the cylinder chamber on the rod side, but the area where is the ring applies which is lower than the piston. According to the concept of pressure, if we keep the strength but decreased the area that applies the pressure increases. This pressure increase is related to the difference in areas, which are called as area ratio factor (R) the ratio of side area between the piston rod side of the annular area.

Because standardization under the ISO, the commercial area ratios for the cylinders are 1.25:1, 1.3:1, 1:6:1, 1.7:1; 1,90:1 , 1,96:1, 2:1, 2,04:1, 2,08:1; 2,1:1 ... However, for non-commercial cylinders, this factor can take very high values \u200b\u200bas 20:1. In the case of equipment mentioned above, the area ratio is 2:1, meaning that the piston area is double the area available on the rod side.

Given this multiplication effect of cylinder pressure differential can make a short analysis of the pressures that arise to either side of the piston when the outflow is throttled to control the speed of the cylinder.

necessary pressure on the piston side (P2) to move the load is equal to the pressure to overcome the load on the cylinder rod pressure to balance the back pressure (P3) generated in the chamber piston rod side.

This counter is basically due to the restriction that the throttle valve offers flow of hydraulic fluid to pass through it.

For the analysis we consider the previous figure, where the charge is positive and the cylinder out.

The power to be exercised by the cylinder is equal to the shit but opposite sign.

On the other hand, the pressure drop at the throttle valve are determined by:

ΔP1 is the loss of pressure from the throttle-return (value usually very low) and ΔP2 is the pressure drop across the choke. In this last expression we have:

and substituting in the equation of force:

But

Substituting we have:

From here:

P3 Solving the general equation, which is the value of pressure that we find, as is the back pressure generated in the piston rod side due to the regulation of the discharge flow, the formula is:

Noting the equation we can deduce that the value of the counter is dependent on load on the cylinder, so that if the load increases, the counter decreases. This makes sense because the pressure on the side of the cylinder piston would be using to beat the charge, ie taking advantage to do the job, if the load can consume the entire value of the pressure on the piston side, then back stem side would be zero, which means no movement, but a completely static condition.

Applying this same logic but reducing the value of the load (Fc) on the cylinder deduce that the counter increases, reaching its maximum value for the case where the cylinder out without charge.

This maximum value is just the value of the pressure factor piston and cylinder areas as we can see, the pressure is multiplied in that factor.

In fact, returning to the introductory fails, pressure in the chamber of the cylinder rod side reached values \u200b\u200bvery close to 300 bar (30 MPa), higher pressure by a factor of 2 to the maximum allowed by the standard for hoses SAE 100 R 2, ie outside the field of security supported by the provision that provides as a safety factor 4 as a minimum.

Applying the same reasoning as above, but to find the value of the pressure side when the cylinder piston retracts, we reach the following expression:

For the return of the cylinder, what happens is a pressure reduction ratio!.

This is the reason why only burst hoses rod side. The solution was simply used to the rod side hoses or exceed the SAE 100 R 11 and that is precisely what was done and the problem disappeared.

This short analysis is not accurate, because certain conditions were disregarded real and drum performance, strength and dead load on the cylinder, however it has enough validity to demonstrate the fails because the values \u200b\u200brecorded in the computer with the usual industrial gauges are almost the same as those calculated.

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THE KALEIDOSCOPE.

THE KALEIDOSCOPE.

A powerful toy that caught my attention was the kaleidoscope. This little gadget was an optical striking effect on my imagination, I spent many hours watching as they appeared and changed the figures that he produced.

much curiosity was aroused in me, I ended screwdriver to get my hands on those beautiful images. I had a disappointment to ensure that these figures do not change that existed in his hand were a few cuts irregular bits of colored plastic, a small tin foil and a tube with a mirror.

40 years after the kaleidoscope continues to exert on me the same fascination that I woke up at that time. Recalling distant memory that I wanted to play the toy for personal enjoyment and that of my daughters. The materials needed for its preparation are easy to find.

Materials:

plastic tube drainage basin, with inner diameter of 1 ½ " x 20 cm in length. Top

a transparent CD holder box.

A CD.

Three strips of mirrors 12 x 2.5 cm.

Accounts (beads, sequins, Swarovski) to make necklaces of various sizes and colors.

The production of the kaleidoscope, the first thing to do is draw on the transparent cover CD holder diameters of the caps to contain the material notions (accounts for necklaces), then cut these discs as shown in the image . The cut was made with a knife, hot enough to melt plastic.

The image below shows these disks.

Because the discs are to be modeled on the measurement of transparent acrylic, the same should be lowered and rounded up to the proper diameter to fit tightly at the ends of the tube. This is done with sandpaper.

smaller diameter disc frosted it, this album does feature frosted diffuser that does not appear in the kaleidoscope of images from the outside when we are looking into it.

plastic tube cut it into two parts as shown. The longest tube length (the one diameter), is slightly greater than the length of the mirrors.

remove burrs from the cutting and place product in the end that has widened the most transparent disk of larger diameter.

introduce in this tube (which you placed the plastic disk) the accounts and beads.

Make this, place the ground disk as a cover, as close to the other drive without dam to the beads. The exact amount of beads and sequins give us the experience we to obtain the fantastic images that reproduce the kaleidoscope.

The three mirrors placed them forming a triangle so that the reflective side faces the inside and join them with silicone or other adhesive.

This prism of mirrors we introduce into the long tube.

Placed mirrors, insert the tube segment containing the beads.

Al CD we cut off the center and to use debase as a cover, 'll look around in the kaleidoscope.

This concludes our kaleidoscope.

With this small kaleidoscope can spend hours enjoying the fantastic images that appear in it.

We can do many tests with the kaleidoscope to obtain many different results, for example by taking longer and placing a bulkhead in the compartment of the beads, obtain other effects not less fantastic.

The number and size of visual elements of color will also alter the optical effect the outcome, so that to achieve good effects have to do several tests and have the patience to do so, but the pleasure that is achieved once perfected our toy is indescribable ... ...

Disclaimer and the images are sharp only in the center of the field of view would be the center of the triangle formed by the mirrors. This distortion or blurring of the reflected images is due to the use of mirrors "normal", where the reflective layer (the silver) is at the bottom of the glass and not on the top, so that the reflections have to go through the glass , where in turn produce additional reflections. As a result we observe the turbidity of the images become more pronounced to the extent that our angle of vision away from the center. This issue is fixed if we use mirrors with the reflective layer on the glass or the mirror substrate.