The present invention pertains to a recirculating respirator for positive pressure operation, in which it is possible to switch off the elements generating the over pressure in case of excessively high oxygen consumption. A flow-measuring device is provided in the oxygen supply line, which is connected to a control unit. A warning device 36, and a switching device, for switching off the over pressure is also provided.

FIELD OF THE INVENTION 
The present invention pertains to a recirculating respirator for positive 
pressure operation including an arrangement for switching off of the 
elements generating the over pressure in the case of excessively high 
oxygen consumption. 
BACKGROUND OF THE INVENTION 
If a leak develops in the system of a recirculating respirator with 
positive pressure operation, e.g., due to the oxygen mask being put on 
incorrectly, the time during which the respirator can be used is greatly 
reduced by the great loss of oxygen caused by the over pressure 
conditions. This may lead to a dangerous situation for the user of the 
respirator. If the device switches over from positive pressure operation 
to normal operation in case of a leak, the loss of oxygen will be reduced. 
Such a respirator has been known from West German Patent No. DE-PS 
32,29,240. This device has a blocking mechanism which eliminates the 
positive pressure operation and is actuated automatically in case of a 
leak. This blocking mechanism is designed as a cylinder-piston unit, 
wherein the movement of the piston is coupled with the movement of the 
breathing bag. At the same time, the force applied by the piston to the 
breathing bag via a lever generates the over pressure in the system. The 
cylinder-piston unit has an outlet valve which opens when a defined stroke 
position of the piston is exceeded, so that the over pressure in a chamber 
above the piston is eliminated and the further supply of pressurized 
oxygen is blocked by an intake valve responding to the pressure reduction 
in the chamber. As a result, the piston no longer applies a force to the 
breathing bag, and the device operates in the normal standard-pressure 
mode. When another defined stroke position of the piston is exceeded, the 
outlet valve is closed and the intake valve is opened, so that the force 
for inducing the positive pressure operation is again available. The 
complicated mechanical design with many sealing members, the lack of an 
unambiguous recognition of a leak from a single, defined position of the 
breathing bag, and the lack of information on the existence of a leak for 
the user of the device are disadvantages of this device. 
SUMMARY AND OBJECTS OF THE INVENTION 
It is an object of the present invention to provide a recirculating 
respirator with automatic over pressure shut-off in the case of a leak, 
which can be realized without complicated mechanical constructions, which 
permits the most unambiguous leak detection possible, and which informs 
the user of the device of the presence of a leak. 
To accomplish this task the device has a flow rate measuring means in the 
oxygen supply line, which is connected to other components. 
The advantages of the present invention are that complicated mechanical 
designs can be dispensed with, leaks can be detected with certainty by 
monitoring the rate of oxygen consumption, and it is possible to warn the 
user of the device of a leak in the breathing circuit. The flow rate 
measuring means detects the rate of oxygen consumption directly at the 
source, without interference with structures and components in the rest of 
the breathing circuit. 
The flow rate measuring means may be designed as a flow sensor of known 
design, for example, a vane type flow sensor. In this case, it is 
preferably arranged in the low-pressure part of the oxygen supply line. It 
is also possible to use as a flow rate measuring means a pressure sensor 
which measures the gas pressure in the oxygen tank, with a downstream time 
integration unit, because if the volume of the oxygen tank is known, the 
rate of oxygen discharged can be inferred from the pressure reduction. A 
residual pressure warning can additionally be realized with the pressure 
sensor. 
The flow rate measuring means is connected to a control unit in which the 
measured flow rate is compared to a preselectable limit value. If the 
measured value exceeds the limit value, the control unit sends a signal. 
This signal can be used to activate a warning device, e.g., a sound 
generator. The user of the device is thus informed of increased oxygen 
consumption. If the increased oxygen consumption is not caused by heavy 
physical activity of the user of the device, he must assume that there is 
a leak in the breathing circuit. If this leak cannot be eliminated, e.g., 
by correcting the position of a slipped mask, the user of the device can 
reduce the loss of oxygen from the respirator by switching off the 
positive pressure operation manually. 
In another variant of the present invention, the signal generated by the 
control unit when the predetermined limit value of the oxygen supply is 
exceeded activates a device which switches off the positive pressure 
operation without involvement of the user of the device. At the same time, 
the warning device is activated in order to inform the user of the device 
of the changed mode of operation of the respirator and the increased 
oxygen consumption. 
The control unit may also be designed to detect two limit values of the 
oxygen consumption. When the first limit value is exceeded, the warning 
device is activated by a signal. The user of the device ca then decide for 
himself whether or not to switch off the positive pressure operation. When 
a second, higher limit value is exceeded, the positive pressure operation 
is switched off automatically. 
In order to clearly distinguish a leak in the system from high oxygen 
consumption by the user of the device, monitoring of the oxygen 
consumption by the flow rate measuring means can be synchronized with the 
phase of expiration of the user of the device. Oxygen consumption detected 
during this phase can only be due to a leak in the system. 
A pressure sensor in the breathing circuit, preferably in the respiration 
gas connection of the user of the device, may serve as a sensor for 
detecting the expiration phase. The pressure in the breathing circuit 
decreases during the inspiration phase and increases again during the 
expiration phase. The expiration phase can be identified from these 
pressure fluctuations, which can be recognized with the pressure sensor. 
The signal of the control unit, which indicates an oxygen consumption 
exceeding a predetermined limit value, is associated with a signal marking 
the expiration phase in a logic circuit, so that an output signal is 
generated only when the limit value of the oxygen consumption is exceeded 
during the expiration phase. This limit value may be selected to be 
substantially lower than in the above-described embodiments of the present 
invention, which do not comprise recognition of the expiration phase. It 
is thus possible to recognize even a small leak in the system. 
A device for switching off the positive pressure operation and a warning 
device can be activated by the above-mentioned output signal of the logic 
circuit. 
It is a further object of the invention to provide a recirculating 
respirator providing both over pressure and normal operation conditions 
which is simple in design, rugged in construction and economical to 
manufacture. 
While a specific embodiment of the invention has been shown and described 
in detail to illustrate the application of the principles of the 
invention, it will be understood that the invention may be embodied 
otherwise without departing from such principles. 
The only figure is a schematic view showing the recirculating respirator 
arrangement according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawing in particular, the recirculating respirator for 
positive pressure operation, is represented schematically in the only 
figure. The components forming the breathing circuit are shown in the 
functional arrangement on a support frame with an outer protective jacket. 
These include a respiration connection 1 with check valves 2, an 
expiration line 3, a regenerating cartridge 4 binding the carbon dioxide 
present in the exhaled air, a breathing bag 5, and an inhalation line 6. 
The oxygen consumed during respiration is replaced from an oxygen tank 7 
serving as the pressurized gas source into the breathing circuit behind 
the breathing bag 5, via a cylinder valve 8, a pressure-reducing valve 9, 
a demand oxygen system 10, as well as via a pipeline 11 with a constant 
metering unit 12. A pressure relief valve 13 positioned behind the 
regenerating cartridge 4 prevents an unacceptably high pressure from 
occurring in the breathing circuit. A pressure gage 15 is connected to the 
oxygen tank 7 via a valve 14 for checking the oxygen reserve. 
The breathing bag 5 consists of bellows 16 closed by a movable, rigid front 
wall 17. 
The over pressure means generating the positive pressure or over pressure 
condition in the breathing circuit are designed as a combination of a 
spring 18 and a single-acting cylinder-piston unit 19 comprising a piston 
20 which is arranged displaceably in a cylinder 21. The cylinder 21 is 
open on the side facing the spring 18, and the displaceable piston 20 is 
connected to the end of the spring 18 facing away from the breathing bag 5 
via a piston rod 22 and the spring plate 23. The other end of the spring 
18 rests on the front wall 17 of the breathing bag 5. 
A partial space 24 of the cylinder, which space is connected to the 
pipeline 11 via a line section 25 and a pressurized gas line 26, is 
located above the piston 20. 
The pressurized gas line 26 contains as a change-over valve, a solenoid 
valve 27 with an actuating magnet 127. By this arrangement the pressurized 
gas line 26 can be closed and separated from the cylinder partial space 
24, wherein the solenoid valve 27, and actuating magnet 127 establishes 
the communication between the cylinder partial space 24 and the breathing 
bag 5 via a vent line 28. The change-over valve can be changed over 
manually by means of a hand lever 29. 
A flow-measuring device or flow rate measuring means 30 is arranged in the 
pipeline 11. It is connected to a control unit 32 via a signal line 31. A 
pressure sensor 33, which is connected to the control unit 32 via a signal 
line 34, is arranged in the respiration connection 1. A sound generator 
36, serving as a warning device, is connected to the control unit 32 via a 
signal line 35, and the solenoid valve 27, and actuating magnet 127 as 
connected to the control unit via signal line 37. 
In the normally occurring positive pressure operation of the respirator, 
the solenoid valve 27, and actuating magnet 127 as connected so that 
oxygen enters the cylinder-piston unit 19 under pressure from the 
pressure-reducing valve 9 via the pressurized gas line 26 and the line 
section 25. As a result, the piston 20 moves into the lower end position, 
thus tensioning the spring 18. The spring 18 therefore applies a force to 
the front wall 17 of the breathing bag 5, as a result of which positive 
pressure builds up in the breathing circuit. 
The amount of oxygen fed through the pipeline 11 into the breathing circuit 
is measured by the flow-measuring device 30 designed as a flow sensor. The 
measured value is sent to the control unit 32 via the signal line 31, and 
is evaluated by a limit value circuit 38. If the measured value exceeds a 
preselectable limit value, the limit value circuit 38 sends a signal to an 
input 39 of a logic circuit 40. 
A pressure sensor 33 , which measures the pressure in the respiration 
connection 1 is arranged in the respiration connection 1 and can be used 
as a respiration phase sensor. The measured value is sent to the control 
unit 32 via a signal line 34 . The pressure rise characteristic of the 
expiration phase of the user of the device is recognized by means of a 
limit value circuit 41 . The limit value circuit 41 sends a signal to the 
second input 42 of the logic circuit 40 during the expiration phase. 
The logic circuit links the two signals on its inputs 39, 42, so that its 
output 43 will carry a signal when the predetermined limit value of the 
amount of oxygen is exceeded during the expiration phase. This signal 
unambiguously marks a leak in the breathing circuit. The output signal of 
the logic circuit 40 activates the sound generator 36 serving as a warning 
device, which is connected via the signal line 35 . The user of the device 
is warned of the presence of a leak in the breathing circuit by the 
acoustic signal of the sound source 36, so that the user is able to try to 
take appropriate countermeasures. At the same time, the solenoid valve 27, 
and actuating magnet 127 are switched over by the output signal of the 
logic circuit 40. As a result, the cylinder partial space 24 is vented, 
the spring 18 is released, and the over pressure in the breathing circuit 
is eliminated, which considerably reduces the oxygen loss caused by the 
leak. Using the hand lever 29, the positive pressure operation can also be 
switched off manually. 
While a specific embodiment of the invention has been shown and described 
in detail to illustrate the application of the principles of the 
invention, it will be understood that the invention may be embodied 
otherwise without departing from such principles.