GB2026617A

GB2026617A - Storage and Adjustment of Hydraulic Pressure

Info

Publication number: GB2026617A
Application number: GB7926264A
Authority: GB
Original assignee: Schloemann Siemag AG
Current assignee: SMS Siemag AG
Priority date: 1978-07-27
Filing date: 1979-07-27
Publication date: 1980-02-06
Also published as: JPS5520993A; DE2832957A1; GB2026617B; FR2433657B1; IT7924671A0; FR2433657A1; IT1207215B

Abstract

Hydraulic operating fluid and compressed gas are contained in a storage vessel 1. The pressure of the gas acts on the hydraulic fluid to drive the fluid to an external device operated thereby. The apparatus makes it possible to alter the gas pressure. A second vessel 14 contains a gas volume communicating with the gas in vessel 1, and a fluid. The fluid quantity in vessel 14 can be increased by pump 24 pumping in more fluid from reservoir 25, or reduced by exhausting fluid via valve 26 and duct 27. The fluid can never be completely drained from vessel 14, and thus a fixed gas volume is trapped in the two vessels, and the pressure of this gas will be increased by pumping more fluid into vessel 14, or reduced by exhausting fluid. <IMAGE>

Description

SPECIFICATION Storage and Adjustment of Hydraulic Pressure The invention relates to the storage and adjustment of hydraulic pressure, and in particular to an apparatus for storing hydraulic pressure, in which hydraulic fluid is acted upon by a gas volume under pressure.

In such a case the gas volume may act, either directly or indirectly, on the operating fluid. In the latter case the gas is separated from the operating fluid either by an elastic separating wall or by a piston. This is particularly necessary when using hydraulic oil as the operating fluid and air as the gas volume, because air can be partly absorbed by the hydraulic oil giving rise to all the known disadvantages.

When the gas is separated from the operating fluid, the gas volume is always in a certain ratio to the fluid volume, and to the operating pressure.

Apart from the increase of volume of the gas upon removal of the fluid, the gas volume and thus the operating pressure is constant. Naturally it is possible to exhaust a portion of the gas volume for the purpose of lowering the pressure.

However, the re-introduction of the gas is possible only by means of an air compressor in a time consuming and expensive manner. Often, however, nitrogen is used as gas volume. It would be very expensive if this gas were exhausted for the purpose of lowering the pressure.

According to the invention, there is provided apparatus for storing hydraulic pressure, comprising a first pressure vessel containing hydraulic fluid for operating an external device, and a gas volume under pressure, and a second pressure vessel also containing a gas volume under pressure and a fluid volume, wherein the gas volumes in both vessels are in communication with each other, and a pump, exhaust valve and safety valve are associated with the second vessel to alter and control the volume of fluid in the second vessel to steplessly vary the pressure of the gas volume in the two vessels to vary the pressure exerted by the gas on the hydraulic fluid.

Although the apparatus is set forth above in its operative state, i.e. containing a gas volume and fluids, the invention extends to the apparatus in the empty condition.

In its upper region containing gas under pressure, the second vessel is connected to the existing gas space in the first pressure vessel.

When a pressure reduction of the operating pressure of the hydraulic fluid is desired, this is effected by exhausting fluid from the second vessel through the exhaust valve. In contrast thereto, when an increase is desired, fluid is fed into the second vessel from a fluid container by means of the fluid pump.

Thus it is possible to adjust the operating pressure in a stepless manner between a maximum value and a minimum value without needed to exhaust the highly-pressurised gas volume, which would be particularly disadvantageous in the case of use of nitrogen as the gas. The maximum fluid pressure corresponds to the highest operating pressure of the apparatus and the minimum value corresponds to the lowest permissible fluid level in the second vessel.

An exhausted quantity of fluid can be replaced again by a pump within a short period of time. By this method storage arrangements can be controlled steplessly as to their pressure. This would be much more difficult to do in the case of an exhausted gas quantity with the prior art system. Moreover the invention permits an adjustment to variable production programmes and a corresponding saving of energy and time.

Furthermore increase of pressure due to heating in the operating pressure system may be compensated without problems by appropriately exhausting pressure fluid from the second vessel.

One embodiment of the invention is explained in detail, by way of example, with reference to the accompanying drawing.

A hydraulic storage vessel 1 is constructed in the form of a so-called piston vessel, the piston 2 being illustrated in bold lines in the lower position.

The upper position is illustrated by a dashdotted line. A hydraulic fluid pressure conduit 3 leads to the consumer. This conduit 3 is also connected by way of valves (not illustrated) to a hydraulic pump (likewise not illustrated) for replenishing hydraulic fluid in the storage vessel 1. Between the piston 2 and the wall of the vessel 1, two seal packings 4a and 4b are provided which effect a seal between the upper, gas filled space 1 a and the lower, hydraulic fluid-filled space 1 b. Between the seal packings there is located a so-called neutral zone 5 which is normally at atmospheric pressure. A conduit 6 leading to the outside makes it possible to recognise if one of the seal packings 4a and 4b is leaky.

A conduit 7 leads from the gas-filled head portion 1 a of the vessel 1 to a plurality of gascontaining pressure vessels 8 each of which may be shut off individually from the conduit 7 by means of shut-off valves 9. Ventilating and dewatering valves 10, respectively, are located at the bottoms of the gas vessels 8.

The conduit 7 between the hydraulic store 1 and the gas stores 8 is provided with a safety valve 11 which exhausts gas if an inadmissibly high pressure is produced in the gas system.

In continuation of the conduit 7 beyond the connections to the gas vessels 8, a conduit 12 leads by way of a shut-off valve 3 to a second, compensating pressure vessel 14. This compensating vessel 14 is equipped with a fluid level indicator 1 6 connected up by way of shut-off valves 15.

From the bottom of the compensating vessel 14, a conduit 1 8 which is connected to a ventilating and de-watering valve 17, respectively, leads to a safety device generally enclosed with a dash-dotted line and denoted by 1 9. The safety device 1 9 consists of a shut-off valve 20, a non-return valve 21 and an electrohydraulic rapid closure valve 22. The safety device 19 serves only to stop the outlet of fluid when the fluid level in the compensating vessel 54 is too iow. When the fluid level drops below a certain point, the rapid closure valve 22 is closed.

The valve 22 is normally energised by means of the electromagnet and is thus open. The closure of the valve prevents gas escaping fron the compensating vessel 14.

A further conduit 23 leads from the safety device 1 9 to a fluid pump 24 with the necessary fittings not illustrated here in detail which is connected to a fluid container 25. A conduit 27 which by-passes the fluid pump 24 and which is provided with an exhaust valve 26 leads likewise from the conduit 23 to the fluid container 25.

A contact manometer 28 is connected by an appropriate shut-off valve to the conduit 18 which leads from the compensating vessel 14 to the safety device 1 9. The contact manometer 28 serves to adjust the pressure within the compensating vessel 14 to any desired value between a maximum and a minimum fluid level. A transmitter 29a is provided for monitoring the maximum pressure corresponding to the highest fluid level, and a transmitter 29b is provided for monitoring the minimum pressure corresponding to the lowest fluid level. The transmitter 29a effects shutting off of the fluid pump 24 when the maximum filling level height in the compensating vessel 14 is exceeded, whereas the transmitter 29b causes the rapid closure valve 22 to close when the fluid level drops to the lowest permissible level in the compensating vessel 14.

When an increase of pressure is desired in the storage vessel 1, the pump 24 delivers fluid into the compensating vessel 14. If the rapid closure valve 22 has previously been closed by the transmitter 29b in consequence of attainment of the lowest fluid level in the compensating vessel 14, the supply of pressure fluid is effected by the pump 24 into the compensating vessel 14 by way of the non-return valve 21, by-passing the closed rapid closure valve 22. Fluid is exhausted to lower the pressure in vessel 1 by opening the valve 26.

Thus the operator controlling the apparatus is in a position to obtain a stepless adjustment of pressure in the storage vessel 1 by exhausting pressure fluid from or feeding pressure fluid into the compensating vessel 14.

The shut-off valve 20 associated with the safety device 1 9 is always open during operation.

Thus shut-off valve 20 is closed only if repairs are necessary at the pump 24 or at other fittings downstream of the valve. Furthermore, a pressure limiting valve 31 is provided as a safety valve in the conduit 30 beyond the fluid pump 24 which terminates in the conduit 23.

Claims

1. Apparatus for storing hydraulic pressure, comprising a first pressure vessel containing hydraulic fluid for operating an external device and a gas volume under pressure, and a second pressure vessel also containing a gas volume under pressure and a fluid volume, wherein the gas volumes in both vessels are in communication with each other, and a pump, exhaust valve and safety valve are associated with the second vessel to alter and control the volume of fluid in the second vessel to steplessly vary the pressure of the gas volume in the two vessels to vary the pressure exerted by the gas on the hydraulic fluid.

2. Apparatus as claimed in claim 1, wherein additional gas-filled pressure vessels communicate with the gas volume in the first pressure vessel.

3. Apparatus for storing hydraulic pressure, substantially as herein described with reference to the accompanying drawing.