JPH07269502A - Oil level detection device within drain pipe in piston type accumulator with back-up cylinder - Google Patents

Abstract

PURPOSE:To detect the amount of leaked hydraulic oil to the side of a gas chamber in the piston type accumulator where a straight hydraulic accumulator is communicated to the gas chamber. CONSTITUTION:A vertical drain pipe 4 is branched out of a connection pipe 3 communicating a back-up cylinder with a gas chamber so as to be installed therein, and a float 24 floating together with a permanent magnet 25 is built in the aforesaid pipe. When the float 24 starts floating with leaked oil forwarded from the gas chamber stored in the drain pipe 4, its oil height is detected by an approaching switch 26 capable of inducing the magnetic force of the permanent magnet 25. Based on the amount of leaked oil, it can be judged whether or not the sealing performance of a piston varying its displacement within a cylinder is good. Therefore, it can be judged in a real time operation base whether or not the replacement of parts such as a piston seal is indispensable without removing an accumulator out of a hydraulic circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for detecting an oil level in a drain pipe in a piston type accumulator with a backup cylinder, and more particularly to a device for detecting an oil level in a cylinder from an oil chamber defined by a piston to a gas chamber beyond the gas chamber. Oil in the drain pipe is designed so that leaked oil that goes to the backup cylinder can be guided to a drain pipe provided between the gas chamber and the backup cylinder, and the amount of drain oil stored in the drain pipe can be detected. The present invention relates to a surface detection device.

[0002]

2. Description of the Related Art An accumulator is used to store and discharge a part of hydraulic oil flowing in a hydraulic circuit to buffer the pressure in a piping system. For example, if the actuator receives an external force and is locked and the hydraulic actuator that drives the actuator cannot operate, the pressure of hydraulic oil sent to the actuator increases excessively. In this case, part of the hydraulic oil is temporarily introduced into the accumulator, and an excessive increase in pressure is avoided to ensure the safety of the hydraulic circuit. On the other hand, when the lock of the actuator is released, the hydraulic fluid accumulated in the accumulator before the hydraulic fluid from the hydraulic pump is supplied to the actuator is immediately discharged to operate the actuator quickly. The pressure can be assisted.

The accumulator includes a bladder type accumulator in which a rubber bladder filled with gas is contained in a shell and a piston type accumulator in which gas is enclosed in one of two chambers defined by a piston in a cylinder. The pressure of the inert gas filled in the bladder or the gas chamber is, for example, 60 kgf / cm ² to 70 kgf /
cm ² . The gas is compressed by a bladder that contracts when hydraulic oil enters the accumulator and a piston that displaces, and the maximum amount is about 210 kgf / cm ² . When the pressure of the hydraulic oil decreases, the gas expands and the hydraulic oil in the accumulator is returned to the hydraulic circuit. In such an operation, the response speed of the bladder type accumulator is slightly faster than that of the piston type accumulator. However, it has a drawback that it causes a sudden rupture accident due to fatigue and damage associated with the expansion and contraction operation of the bladder.

[0004]

In recent years, with the increase in size and capacity of hydraulic actuators, the accumulator pressure storage capacity may be increased. In this case, the number of accumulators installed is increased or a large-capacity accumulator is introduced. In the former case, the existing accumulators are arranged by arranging a plurality of such accumulators, but the cost of the hydraulic system tends to increase.
Since the latter is realized by attaching a plurality of backup cylinders to the accumulator, the equipment cost can be reduced. That is, a plurality of direct pressure type accumulators are communicated with the gas chamber of the piston type accumulator, thereby substantially expanding the volume of the gas chamber.

In the case of a bladder type accumulator, it is usually impossible for hydraulic oil to enter a rubber bladder containing gas. On the other hand, in the piston type accumulator, the oil chamber and the gas chamber are defined by the piston, so that the hydraulic oil, even if only slightly, enters the gas chamber through the space between the piston and the cylinder. When the accumulator becomes large, the diameter of the piston also becomes large, and the sealing performance is likely to be degraded by the piston seal, and leakage is even more difficult to avoid. The hydraulic fluid that leaks past the piston accumulates in the gas chamber or adheres to the inner surface of the cylinder. However, since the function of the accumulator does not drop sharply while hydraulic oil leaks for a short time, and there is no way to detect the amount of leaked oil, it is necessary to perform regular maintenance work such as disconnecting the accumulator from the hydraulic circuit. Is often neglected. Furthermore, in the case of a piston type accumulator with a backup cylinder, the backup cylinder functions to expand the capacity of the gas chamber, so the effect of leaked oil is small. In this case, the presence or absence of leakage and the amount of leakage cannot be monitored on a daily basis, and it is not easy to detect a decline in the pressure accumulation function at an early stage. Therefore, there is a problem that the time interval of the maintenance work has to be shortened, and as a result, the hydraulic equipment must be frequently stopped. By the way, if the piston seal deteriorates during long-term use, not only the hydraulic oil will leak to the gas chamber and backup cylinder, but also the gas in the gas chamber will leak into the oil chamber, making the hydraulic oil cloudy and Not only will the function be impaired, but the driving of the actuator will also be adversely affected.

The present invention has been made in view of the above problems, and an object thereof is to leak to the gas chamber side while the piston type accumulator in which the gas chamber is connected to the backup cylinder via the connecting pipe is in the operating state. It is possible to detect the amount of drain oil that has leaked and to directly and accurately grasp the level of the drain oil that has leaked, so that the seal function of the piston can be judged and the maintenance work of the accumulator can be reduced. To provide an oil level detecting device in a drain pipe in a piston type accumulator with a backup cylinder.

[0007]

SUMMARY OF THE INVENTION According to the present invention, a cylinder having a closed space formed by a head cover and a bottom cover is defined by a piston, and a gas chamber on the head cover side has an oil chamber on the bottom cover side connected to a hydraulic circuit. The present invention is applied to a piston type accumulator device in which a gas for restoring the position of the piston displaced by the change in the volume is filled, and the gas chamber is connected to the backup cylinder via a connecting pipe. The characteristic feature is that, with reference to FIGS. 1 and 2, since the hydraulic oil that leaks from the oil chamber 9 over the piston 8 to the gas chamber 10 and further enters the backup cylinder 2 is stored, The non-magnetic drain pipe 4 which is closed is branched from the connecting pipe 3 and hangs down. The drain pipe 4 has a built-in float 24 that floats on the oil surface along with a permanent magnet 25, and a magnetic sensitive body 26 that is sensitive to the permanent magnet 25 is arranged in the drain pipe 4.

The magnetic responsive body is preferably a proximity switch mounted on the outer surface of the drain pipe 4 and operated by the permanent magnet 25.

Referring to FIG. 5, the magnetic responsive body vertically penetrates the center of the float 24 and generates a torsional strain on the magnetostrictive line when the permanent magnet 25 approaches the magnetostrictive linear displacement sensor 31. Alternatively, the probe rod 32 may be used.

Further, referring to FIG. 8, the magnetic responsive body is a magnetic sensitive iron piece 45 which is displaced by being attracted to the permanent magnet 25 in a non-magnetic guide pipe 46 which vertically penetrates the center of the float 24. You can also leave it. In that case, the magnetism sensitive iron piece 45 may be hung on the cable 43 of the potentiometer 44 that converts the length of the unrolled wire into an electric resistance value to detect the height of the drain oil surface.

[0011]

[Operation] When the pressure in the hydraulic circuit rises, the accumulator 1
Hydraulic oil enters the oil chamber 9 of the backup cylinder 2 and the piston 8 rises, so that the backup cylinder 2 via the gas chamber 10 and the connecting pipe 3
The enclosed gas inside is compressed. When the pressure of the hydraulic circuit is lowered, the hydraulic oil in the oil chamber 9 is discharged by the expanding gas. If the sealing function of the piston 8 is lowered in such an operation, hydraulic oil in the oil chamber 9 leaks to the gas chamber 10. When the gas accompanied by the leaked oil passes through the connecting pipe 3, the atomized hydraulic oil flows down and is stored in the drain pipe 4. When the amount of staying oil increases, the float 24 floats up, and the permanent magnet 25 accompanying it floats the magnetic sensitive body. The position of the float 24 is detected depending on the presence or absence of the sensitivity, and thus the quality of the sealing function between the piston 8 and the cylinder 7 can be known.

If the magnetic sensor is the proximity switch 26,
The position of the permanent magnet 25 is detected for each of the mounted parts, and the oil height is grasped. If a plurality of proximity switches are attached, detection is performed for each position. If the mounting position is changed, detection at any position is possible.

When the magnetostrictive linear displacement sensor 31 is used, the magnetic force of the permanent magnet 25 causes the probe rod 3 to move.
Torsional strain can be applied to the second magnetostrictive line, and the height of the stored oil surface can be continuously detected.

When the potentiometer 44 is used, the magnetic sensitive iron piece 4 suspended from the cable 43 is then used.
5 moves up and down by a permanent magnet 25 that moves with the float 24. The position of the float 24 can be known from the electric resistance value corresponding to the payout length of the cable 43, and the drain oil amount corresponding thereto can be grasped.

[0015]

According to the present invention, the amount of rise of oil in the drain pipe can be detected in real time, that is, without removing the accumulator from the hydraulic circuit. Based on that, the quality of the piston seal function is judged,
The maintenance work of the accumulator can be reduced.

If the proximity switch is attached to the drain pipe, it can be detected that the oil level has reached the mounting position. By disposing a plurality of proximity switches, detection at each desired position becomes possible. Further, it is possible to detect even at an arbitrary position by changing the mounting portion of the proximity switch. When a magnetostrictive linear displacement sensor or a potentiometer is adopted, the oil height can be continuously detected, and it is possible to obtain a highly reliable piston type accumulator device that can easily predict long-term maintenance management.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An oil level detecting device in a drain pipe in a piston type accumulator with a backup cylinder according to the present invention will be described in detail below based on embodiments. Figure 2
FIG. 3 is an overall configuration diagram of a piston type accumulator in which a large number of backup cylinders are connected to each other to increase the volume of a gas chamber defined by a piston. This is composed of a piston type accumulator 1 and a gas cylinder 2 which is a direct pressure type accumulator. A drain pipe 4 is attached in the middle of a connecting pipe 3 which connects them, and leaks from an oil chamber 9 over a piston 8 to a gas chamber 10. The hydraulic oil is collected before reaching the backup cylinder 2.

As shown in FIG. 3, the piston type accumulator 1 is constructed by defining a cylinder 7 in which a closed space is formed by a head cover 5 and a bottom cover 6 into an oil chamber 9 and a gas chamber 10 by a piston 8. To be done. The oil chamber 9 on the bottom cover side is connected to a hydraulic circuit (not shown), and the gas chamber 10 on the head cover side is filled with gas for restoring the position of the piston 8 displaced by the volume change of the oil chamber 9. The gas is an inert gas with no risk of explosion, and nitrogen gas or argon gas is used.
The gas chamber 10 is of a direct pressure type through the pressure cover 12 closed by the top cover 11 and the connecting pipe 3 connected to the gas chamber 10 in order to increase the amount of the enclosed gas and increase the pressure storage capacity. It is in communication with the accumulator.

As shown in FIG. 2, the connecting pipe 3 includes a communicating pipe 13 connected to the backup cylinder 2 and a communicating pipe 1 thereof.
3 is connected to the gas chamber 10 by a horizontal connecting pipe 14. The communication pipe 13 is, for example, 4 as shown in FIG.
8 stacked in a row and fixed to the frame member 16 with the band 15
The books are arranged vertically to connect the direct pressure type accumulators 2, 2. Then, the branch pipes 19 and 19 extending horizontally to the left and right and the respective backup cylinders 2 are communicated with each other through four joints 18 attached below the stop valve 17. The connection pipe 14 is connected to the pressure cover 12 and extends horizontally as shown in FIG. 2, and is connected to the communication pipe 13 via the connector 20 at the tip thereof. In the middle of the connecting pipe 14, the drain pipe 4 is hung down via a branch fitting 21 (see FIG. 1), and the drain pipe 4 is pulled from the oil chamber 9
The hydraulic fluid that has leaked into the gas chamber 10 beyond the above can be captured and stored before entering the backup cylinder 2. The drain pipe 4 can discharge the accumulated drain oil,
The lower end is normally closed and covered with a cap 22.

As shown in FIG. 1, an oil-resistant float 24 is floated on the liquid surface of the drain oil 23. This is a plastic foam in which glass micro hollow spheres and high-strength epoxy resin are combined. Then, the permanent magnet 25 is attached to the outer peripheral side of the float 24 by being fitted or molded, and the proximity switch 2 as a magnetic responsive body attached to the outer surface of the drain pipe 4.
6 and 26 are operated. That is, the proximity switch 26 in which the contact 26a is closed by the permanent magnet 25
From A, the liquid height H of the drain oil 23 floating in the float 24 can be detected. The drain pipe 4 is made of a non-magnetic material such as a stainless steel material or a plastic material, and is designed so as to prevent the permanent magnet 25 from magnetizing and prevent the sensitive operation of the proximity switch 26 from being disturbed.

According to this structure, the amount of drain oil is detected and the amount of hydraulic oil leaked to the gas chamber side in the piston type accumulator 1 is known in the following manner to determine whether the sealing function of the piston 8 is appropriate. can do. When the pressure of the hydraulic circuit rises, the hydraulic oil enters the oil chamber 9 from the oil passage 27a of the cylinder base 27 shown in FIG. 3 via the oil passage 6a of the bottom cover 6 and pushes up the piston 8 to push up the gas chamber 10. The fill gas is compressed. Since the gas chamber 10 is connected to the plurality of backup cylinders 2 and 2 and its volume is substantially expanded, a large amount of hydraulic oil can be stored in the accumulator 1 even when the pressure increase of the hydraulic oil in the hydraulic circuit is not large. The pressure can be stored in.

When the pressure of the hydraulic oil is lowered, the gas is expanded and the piston 8 is lowered, so that the hydraulic oil is returned to the circuit. While repeating such operations for a long time,
When the seal function deteriorates due to wear of the piston seal 8a and the wear ring 8b mounted around the piston 8, hydraulic oil in the oil chamber 9 will pass over the piston 8 and the gas chamber 10
Leak to. The leaked oil that moves along with the flow of gas generated by the movement of the piston 8 is atomized into droplets or the like, and the gas chamber 10
From the head cover 5 to the backup cylinder 2 via the gas passage 5a of the head cover 5 and the gas passage 12a of the pressure cover 12.
However, when the horizontal connecting pipe 14 shown in FIG. 2 is moved, the hydraulic oil drops at the branch fitting 21 onto the vertical drain pipe 4. When hydraulic oil accumulates in the drain pipe 4,
The float 24 floats on the oil surface. When the amount of drain oil 23 increases, the float 24 floats and the proximity switch 26A
Is contacted by the magnetic force of the approaching permanent magnet 25.
Close. By looking at the sensitive operation of the proximity switch 26A with a switch panel or the like, it is possible to know where the drain pipe 4 has the liquid surface of the drain oil 23.

When a plurality of proximity switches 26 are attached vertically as shown in the figure,
The amount of accumulated oil is detected one by one. Also, by comparing the time from the first proximity switch to the operation of the next proximity switch with the time from the operation of the next proximity switch in the same interval, that is, comparing the rising speed of the liquid level. For example, the extent of the leakage can be grasped. Since the proximity switch 26 is provided outside the drain pipe 4, the proximity switch can be appropriately moved up and down, and it is possible to detect that the oil level has risen at an arbitrary position. The increase in the liquid level of the drain oil 23 means that the sealability between the piston 8 and the cylinder 7 is deteriorated, and the piston seal 8a and the wear ring 8b are being worn. The same applies when it is determined that the leak rate is high even if the oil level is low. In this way, it is confirmed that the sealing function of the piston 8 has deteriorated. Therefore, before the function of the accumulator 1 deteriorates, the piston seal 8a
Etc. can be replaced to restore the function. The oil stored in the drain pipe 4 is
It is discharged by removing (see FIG. 1) and opening the drain port fitting 28.

FIG. 5 shows an example in which a magnetostrictive linear displacement sensor 31 is adopted instead of the proximity switch. That is, as the magnetic sensitive body sensitive to the permanent magnet 25, the float 24
A probe rod 32 is used which penetrates the center of the drain pipe 4 and extends almost the entire length of the drain pipe 4. The magnetostrictive linear displacement sensor 31 generates a torsional strain on the magnetostrictive wire applied to the probe rod 32 by the approach of the permanent magnet 25 which is displaced along with the float 24, and the float 2
4 positions can be obtained. Therefore, torsional strain can be generated regardless of the position of the permanent magnet 25, and the liquid level of the drain oil 23 is continuously detected via the lead wire 33. The permanent magnet 25 is attached to the inner peripheral side of the float 24 so as to face the probe rod 32. By the way,
In order to mount the probe rod 32, its upper end is fixed to the branch fitting 21. The lower end is supported by a perforated spacer 34 fixed to the inner surface of the drain pipe 4 so that the movement of the float 24 that moves up and down along it is not obstructed, that is, the probe rod 32 does not tilt.

In the magnetostrictive linear displacement sensor 31 thus mounted, the position of the oil surface is detected as follows. Probe rod 32 in the drain pipe 4
From the main body 31A of the magnetostrictive linear displacement sensor 31 connected to the lead wire 33, a current pulse in the direction of arrow 35 in FIG. 6 is applied to the probe rod 32 forming the magnetostrictive wire 32A at regular time intervals. By applying this current pulse, the circumferential magnetic field 36 is applied to the entire region of the magnetostrictive line 32A in the axial direction.
Occurs momentarily. When the permanent magnet 25 is at the position shown in the figure and exerts a magnetic force, an axial magnetic field 37 shown by a broken line is generated in the vicinity thereof.
Is given. This axial magnetic field 37 and circumferential magnetic field 36
A gradient magnetic field 38 like a thick line is generated by the synthesis of
The magnetostrictive line 32A is distorted in the inclination direction. This torsional distortion occurs only at the moment when the current pulse is applied, and this becomes a mechanical elastic wave and propagates on the magnetostrictive line 32A toward both ends thereof.

When a current pulse 39 is generated at a certain time interval as shown in FIG. 7A, an induction signal 40 due to the current pulse 39 appears as shown in FIG. 7B, and a mechanical elastic wave is generated t seconds later. Distortion signal 4 indicating arrival of ultrasonic waves
1 is a strain detector 31B provided on the main body 31A (see FIG. 5)
Detected in. If the distance from the strain detector 31B to the position of the permanent magnet 25 is S and the propagation velocity of ultrasonic waves is v,
It is expressed as S = v · t. On the other hand, mechanical elastic waves are transverse waves due to the propagation of torsional strain. Its propagation speed v
Is the density ρ of the magnetostrictive line and the rigidity factor G of the magnetostrictive line, v =
It can be expressed as √ (G / ρ). Therefore, the above-mentioned distance S is t · √ (G / ρ), and the distance S can be immediately obtained by measuring the time t required for propagation in the main body 31A.

In this way, how far the position of the permanent magnet 25 is from the strain detector 31B is measured, and the distance can be displayed on the CRT or the like.
The position of the permanent magnet 25 can be continuously detected each time a current pulse is applied, and the displacement of the float 24 can be constantly monitored. That is, it can be seen that when hydraulic oil in the oil chamber 9 crosses the piston 8 and enters the gas chamber 10 and a large amount of it is accumulated in the drain pipe 4, the piston seal 8a and the like are abraded.

FIG. 8 shows an example in which a potentiometer 44 for converting the pay-out length of the cable 43 into an electric resistance value to detect the height of the drain oil surface is used. The potentiometer 44 is attracted to the permanent magnet 25 as a magnetic sensitive body. Magnet-sensitive iron piece 4 that moves up and down
5 is adopted. Therefore, a non-magnetic guide pipe 46 extending vertically through the center of the float 24 is arranged in the drain pipe 4, and a space for displacing the magnetic sensitive iron piece 45 is secured. The lower end is closed so that drain oil does not enter the guide pipe 46, but the upper end penetrates the branch metal fitting 21 up and down and is open to the atmosphere, and the cable 43 that suspends the magnetic sensitive iron piece 45 is connected to the guide pipe 46. It can be guided to the potentiometer body 44A. Although not shown in the figure, the cable 43 is provided in the main body 44A of the potentiometer by utilizing the elastic force of a vine spring.
There is a pulley that can be wound up. Therefore, when the magnetism sensitive iron piece 45 is lowered by the permanent magnet 25, the cable 43 is paid out from the pulley, and when it is raised, the cable 43 is wound. The rotation of the pulley that winds up the cable 43 is converted into one rotation or less by the planetary gear mechanism, and an output voltage corresponding to the electric resistance value obtained at that rotation angle can be obtained. Therefore, the magnetic sensitive iron piece 4
Since the position of No. 5 is grasped, the amount of stay of the drain oil 23 can be known. The guide pipe 46 must be held in a vertical posture in order to make the movement of the float 24 smooth and accurate. Although not shown in the figure, such as the perforated spacer 34 (see FIG. 5) described above,
The guide pipe 46 is supported below the drain pipe 4.

As can be seen from the description of any of the above examples, the piston type accumulator, which connects the backup cylinder to the gas chamber via the pipe, does not leak from the hydraulic piping system and leaks to the gas chamber side during operation. The amount of oil taken can be detected. Whether or not the piston sealing function is good or bad can be grasped by the amount of the oil amount or the rate of increase, and the maintenance work of the accumulator can be reduced. That is, it becomes possible to easily know whether or not the piston seal or the like needs to be replaced. In particular, when a magnetostrictive linear displacement sensor or potentiometer is used, the oil height can be continuously detected, which makes it easier to predict maintenance in the long term. Thereby, a highly reliable piston type accumulator can be obtained.

[Brief description of drawings]

FIG. 1 is an enlarged cross-sectional view of a drain pipe equipped with a proximity switch, which is an example of a magnetic sensor, showing a main part of an oil level detecting device in a drain pipe according to the present invention applied to a piston type accumulator with a backup cylinder.

FIG. 2 is an overall configuration diagram in which a piston type accumulator having a backup cylinder is equipped with a drain pipe.

FIG. 3 is an internal structure diagram of a piston type accumulator.

4 is a view taken along the line IV-IV in FIG.

FIG. 5 is a cross-sectional view of a drain pipe including a partially enlarged portion equipped with a magnetostrictive linear displacement sensor.

FIG. 6 is a diagram showing the principle of generation of torsional strain in the magnetostrictive line of the probe rod.

FIG. 7A is a time chart showing generation of a current pulse applied to a magnetostrictive line with time as a horizontal axis, and FIG. 7B.
Is a time chart showing the time lag between the induction signal due to the current pulse and the arrival signal of the mechanical elastic wave detected thereafter.

FIG. 8 is a cross-sectional view of a drain pipe including a partial enlargement equipped with a potentiometer.

[Explanation of symbols]

1 ... Piston type accumulator, 2 ... Backup cylinder, 3 ... Connection pipe, 4 ... Drain pipe, 5 ... Head cover, 6 ... Bottom cover, 7 ... Cylinder, 8 ... Piston,
9 ... Oil chamber, 10 ... Gas chamber, 21 ... Branch metal fitting, 23 ... Drain oil, 24 ... Float, 25 ... Permanent magnet, 26 ... Proximity switch (magnetic sensitive body), 31 ... Magnetostrictive linear displacement sensor, 32 ... Probe Rod (magnetic sensitive body), 43 ... Cable, 44 ... Potentiometer, 45 ... Magnetosensitive iron piece (magnetic sensitive body), 46 ... Guide pipe, H ... Oil height.

Claims (4)

[Claims] 1. A cylinder defining a closed space formed by a head cover and a bottom cover is defined by a piston, and the piston is displaced in the gas chamber on the head cover side due to a change in volume of an oil chamber on the bottom cover side connected to a hydraulic circuit. In a piston type accumulator device in which a gas for restoring the position of is sealed, and the gas chamber is communicated with a backup cylinder via a connecting pipe, the gas chamber leaks from the oil chamber over the piston into the gas chamber, and further In order to store the hydraulic oil that is about to enter the backup cylinder, a non-magnetic drain pipe with its lower end closed is branched from the connecting pipe and hangs down, and the drain pipe floats on the oil surface along with a permanent magnet. A float is built in, and a magnetic responsive body that is sensitive to the permanent magnet is arranged in the drain pipe. Oil level detection device in drain pipe of piston type accumulator with backup cylinder. 2. The piston type accumulator with a backup cylinder according to claim 1, wherein the magnetic responsive body is a proximity switch attached to an outer surface of the drain pipe and operated by the permanent magnet. Oil level detector in drain pipe. 3. The magnetic sensitive body is a probe rod of a magnetostrictive linear displacement sensor, which vertically penetrates the center of the float and generates a torsional strain in a magnetostrictive line when the permanent magnet approaches. The oil level detecting device in the drain pipe in the piston type accumulator with a backup cylinder according to claim 1. 4. The magnetically sensitive body is a magnetically sensitive iron piece that is displaced by being attracted to the permanent magnet in a guide pipe of a non-magnetic material that vertically penetrates through the center of the float, and the magnetically sensitive iron piece is drawn out. The drain in the piston type accumulator with a backup cylinder according to claim 1, wherein the drain is suspended from a cable of a potentiometer that detects the height of the drain oil surface by converting the length of the drain into an electric resistance value. Pipe oil level detection device.