GB2044411A - Pump with pressure relief valve - Google Patents

Abstract

The pump includes a motor shaft (5) driving a pump shaft (2), in which is formed an internal passage (3) for supplying lubricating fluid, the passage having a closure device (10) which is adapted to be held closed by centrifugal force acting on a bell-crank (9) while the shafts are rotating, so as to form a pre-loaded pressure-relief valve. <IMAGE>

Description

SPECIFICATION Pump with pressure-relief valve The invention relates to a pump having a pressure-relief means which is particuiarly suitable for use in apparatus having single-conduit lubrication systems.

With single-conduit lubrication systems all lubricating positions or points are supplied with a quantity of lubricant suitable for the respective lubrication point and at prescribed time intervals by a pump being switched on for a brief period.

For the dosage or measurement of this quantity of lubricant, each lubrication point has associated therewith a dosing or measuring valve, which is moved from its normal position with the build up of the lubricant pressure and thereby delivers the quantity of lubricant which corresponds to its dosage volume. As soon as it is assured, for example, by monitoring the lubricant pressure, that all measuring valves have become operative, the pump is switched off again. So as to facilitate the return of the measuring valves to their normal position, the ievel of lubricant pressure remaining in the circuit or pipe between the pump and the measuring valves has to be reduced or the lubricant pipe or circuit has to be relieve of pressure.

In order to relieve the pressure of the lubricant circuit, it is known to incorporate into the latter an electrically operated valve, which shuts off a return flow pipe to the lubricant container when the pump is switched on, the said pipe being opened again when the pump is switched off.

With the valve opened, the pressure in the lubricant pipe can be released; the measuring valves are able to be re-set.

It is already known to provide à centralised lubrication system, in which a sliding control valve is positioned in the lubricant pipe leading from a pump to the dosage valves or measuring devices, the said slide valve having connected thereto a return line with non-return or check valves. When the pump is switched on, the control valve, due to the lubricant pressure which is being built up, first of all opens the connection to the measuring valves. After all measuring valves have completed their delivery of lubricant, the pressure in the lubricant circuit or pipe rises again. Due to this increased pressure, the said slide valve opens the connection to the return line or pipe, so that the lubricant circuit or pipe can be relieve of load, while simultaneously the pump is switched off again.The check valve in this case ensure that a predetermined basic pressure is maintained in the lubricant pipe, which pressure does not, however, influence the re-setting of the measuring valves.

These known pressure-relieving means have the disadvantage that additional parts and more especially the connection of a return line are necessary in the construction of the lubrication system. The danger also exists with these pressure-relieving means that they do no function satisfactorily with very small delivery quantities, in the region of between 0.1 I/hand 51/h. The said arrangement is particularly sensitive to dirt and temperature differences (viscosity) and is costly.

The present invention accordingly seeks to provide a pump with a pressure-relief means, more especially for single-circuit lubrication systems, with which a satisfactory relief of the pressure in the lubricant pipe can be guaranteed, without any great expense and also with smallest possible delivery quantities. Accordingly the present invention provides a fluid pump including a motor shaft driving a pump shaft, and in which the pump shaft is formed with an internal passage for supplying lubricating fluid, the passage having a closure device which is adapted to be held closed by centrifugal force while the shafts are rotating, so as to form a pre-loaded pressure-relief valve. As a result of this construction, it is possible to ensure that the lubrication pipe or circuit is always relieved of load after switching off the pump, and no additional return line is necessary in this case.

One embodiment of the invention will now be described by way of example with reference to the accompanying drawing which is a partially sectional view of a pump having a pressurerelieving device.

The drawing shows the housing 1 of a pump which may, for example, be constructed as a gearwheel pump, a piston pump or the like. Rotatably mounted in the housing 1 is a pump shaft 2 which, in this constructional example, comprises a duct or passage 3 opening on the driving side of the pump shaft 2, which passage, in a manner known per se but not illustrated, has a flow connection with the lubricant pipe or circuit. In the region of the pump shaft, the housing comprises a cylindrical cove 4, into which projects the shaft 5 of a motor which is not shown.

Fixed on the shaft 5 is a coupling sleeve, which has a transverse groove 7 in its end which faces the end of the pump shaft 2, the said pump shaft being formed with flats on its end which drivingly engage in the groove, so as to form a dog-clutch.

Pivotally mounted in this transverse groove 7 on a journal 8 is bell crank arm 9, whose free arm 9a extends parallel to the shaft 5. The end surface of the crank arm 9 which faces the pump shaft 2 acts on a ball valve closure member 10 held in a turned recess 11 at the mouth of the passage 3, the said recess being machined to form a sealing seat. The mounting of the bell crank arm 9 is so arranged that a force is exerted on the closure member 10 when the crank arm is swivelled in a clockwise direction as seen in the drawing.

The closure member 10, either by itself or in conjunction with the inherent weight of the elbow layer 9, exerts a closing force of such a size that the passage 3 is sealed off sufficiently firmly to maintain a specified basic pressure of the lubricant with the pump stationary. When the pump is switched on, there is a tendency for the elbow lever 9 to swing in a clockwise direction, due to centrifugal force. The result of this is that the force with which the closure member is pressed against its sealing seat is increased, so that when the pump is running, the passage 3 is always closed off with respect to the lubricant pressure.With the pump switched off, the component of pressure caused by centrifugal force on the closure member falls to zero and the lubricant pressure built up in the lubricant pipe during the delivery operation can be relieved by delivery of extremely small amounts of lubricant through the passage 3 and, as a result, the lubricant pipe is relieved completely or until the basic pressure is reached.

The lubricant flowing over from the passage 3 flows back through a bore 12 in the housing 1 into the lubricant container.

The mass of the bell crank arm 9 and thus the centrifugal force being established at the rated speed of rotation of the pump can be so chosen that when a permissible lubricant pressure is exceeded, the closure member is lifted from its closure position by this lubricant pressure, against the force of the arm 9, so that the increased lubricant pressure can be reduced and any damage to parts of the lubrication plant is avoided.

Claims (7)

1. A fluid pump including a motor shaft driving a pump shaft, and in which the pump shaft is formed with an internal passage for supplying lubricating fluid, the passage having a closure device which is adapted to be held closed by centrifugal force while the shafts are rotating, so as to form a pre-loaded pressure relief valve.

2. A fluid pump as claimed in claim 1 in which the closure device comprises a ball-valve.

3. A fluid pump as claimed in claim 1 or claim 2 in which the closure device is held closed by a pivotable lever mounted on a rotating part of the pump which is adapted to swing about its pivot under the influence of centrifugal force so as to engage the closure device.

4. A fluid pump as claimed in claim 3 in which the said lever comprises a bell-crank lever which is pivotally mounted at one end of one arm for rotation about a pivot mounted perpendicular to the axis of said motor shaft and connected to said motor shaft, the other arm of the lever being arranged to lie substantially parallel to the axis of said shaft as that the lever swings outwardly when the shaft rotates; the said closure device being arranged adjacent said lever so as to be engaged by one of the arms of said lever.

5. A fluid pump as claimed in claim 4 in which the motor shaft and the pump shaft are coaxial and are drivingly engageable by means of a dogclutch comprising a diametral groove in the end face of the motor shaft and a pair of co-operating parallel flats on the corresponding end face of the pump shaft; the bell crank lever being journalled on a shaft mounted across said groove, and the ball-valve being mounted in the facing end surface of said pump shaft,

6. A fluid pump as claimed in any preceding claim in which the closure device is arranged to open at a predetermined operating pressure of the pump.

7. A fluid pump substantially as herein described with reference to the accompanying drawing.