Fluid circulating heating pad
United States Patent 3894213

A fluid heating and temperature control unit is provided for a system utilizing a circulating fluid type heating pad or thermal blanket. The unit comprises a bulkhead with a fluid reservoir mounted below and a cover mounted above including means for directing the flow of ventilating air. The bulkhead carries a heater extending into the reservoir, a fluid circulator and a thermostatic temperature control device including a sensor having channels, one of which carries inflowing fluid and the other of which carries outgoing fluid so that the control of temperature is responsive to both inflowing and outflowing fluids, substantially to the average temperature thereof. In this manner a more satisfactory control of temperature of the heating pad is achieved than if the control were made responsive either to the temperature of the hotter fluid flowing into the pad or the cooler fluid returning therefrom.

Application Number:
Publication Date:
Filing Date:
Primary Class:
Other Classes:
126/204, 165/46, 219/212, 219/528, 392/451, 392/485, 607/104
International Classes:
A47C21/04; F24H1/20; G05D23/275; H05B3/34; (IPC1-7): F24H1/20
Field of Search:
219/212,296-298,306,315-316,528 126
View Patent Images:
US Patent References:
2982841Improved heating and temperature control method and apparatus for personal thermal systems1961-05-02MacCracken
2885189Personal thermal devices1959-05-05MacCracken
2866072Thermal blanket circulating and control means1958-12-23Smith
2802088Heating units1957-08-06MacCracken
1896953Electric ice cap1933-02-07Hassell

Primary Examiner:
Albritton C. L.
Attorney, Agent or Firm:
Knobbe, Martens, Olson, Hubbard & Bear
What is claimed is

1. In a controlled-temperature circulating fluid system:

2. In a controlled-temperature circulating fluid system:

3. In a controlled-temperature circulating fluid system:

4. Apparatus as described in claim 2 including a temperature limiting device responsive to temperature of fluid in the reservoir.

5. Apparatus as described in claim 4 wherein the temperature limiting device includes a probe extending through the bulkhead into the fluid reservoir.

6. Apparatus as described in claim 4 wherein the temperature limiting device is adapted to operate at a higher temperature than said first mentioned temperature control device.


Thermal blankets and heating pads, particularly for use for patients in hospitals, have been proposed in which a warmed or heated fluid circulating through ducts of a pad or blanket is utilized instead of an electric blanket or heating pad having resistance wires imbedded in the blanket or pad. Such circulating fluid heating or warming devices avoid the hazard of electrical circuits in close proximity to a patient or a sleeping person with the attendant hazards of fires in the event of short circuits or electrical shock in the event of defective insulation or the accidental connection of the supply circuit to a high voltage source.

However, for use in hospitals such apparatus must operate reliably without excessive need for attention in order to conserve nurses' time and must not introduce other hazards.

It is accordingly an object of the invention to provide a circulating fluid system which is simple in operation, light and compact, readily transported from one location to another, which maintains a desired temperature without attention, without regard to movement of the patient or the patient's position in relation to the warming pad or blanket and which is free from hazards in the event of stoppage of flow of fluid through the apparatus as a result of a leak in the pad or blockage in one of the passageways.

Other and further objects, features and advantages of the invention will become apparent as the description proceeds.


In carrying out the invention in accordance with a preferred form thereof a compact unitary construction is employed for fluid heating and temperature control apparatus for connection to a heating pad of the circulating fluid type. The fluid heating and control unit comprises a bulkhead with the elements of the unit mounted thereon, a fluid reservoir mounted below the bulkhead and a cover or hood mounted above the bulkhead. A fluid heater is mounted on the bulkhead with an electric heating element extending downward through the bulkhead into the fluid reservoir.

A temperature sensor is also mounted on the bulkhead containing two channels one of which is connected to an output port and the other to an inlet port for connection to inlet and outlet tubing from the heating pad. There is a pump or fluid circulator having an output port connected to one of the channels of the sensor and an inlet port connected to tubing dipping into the reservoir. An adjustable thermostat is provided which is in temperature-conducting relationship to the sensor so that it is responsive to both the inflowing and outflowing fluid temperatures of the heating pad. In addition there is an overload or temperature-limiting thermostat having a probe extending into the reservoir. These thermostats have contacts connected in series with the electric heating element and an electric power supply so that the sensor thermostat regulates the temperature produced by the heating element and the temperature-limit thermostat turns off the electric power supply in the event that temperature in the reservoir becomes excessive as a result of stoppage of fluid flow resulting from loss of fluid from the pad or plugging up of one of the lines. The circulating pump also carries a fan so arranged as to create a movement of air from the temperature sensor to the heater so that the sensor remains unaffected by direct radiation, conduction or convection of heat from the heater.

A better understanding of the invention will be afforded by the following detailed description considered in conjunction with the accompanying drawings.


In the drawings:

FIG. 1 is a perspective view of the assembly of a temperature heating and temperature control unit connected by tubing to a heating device of the circulating fluid type such as a fluid blanket for use in cold climates or in hospitals or a heating pad or the like;

FIG. 2 is a plan view of the fluid heating and temperature control unit with the cover removed to expose elements of the unit mounted upon a bulkhead;

FIG. 3 is a view of an elevation of the apparatus of FIG. 2 with the cover and fluid reservoir represented as cut by a vertical plane 33 through the center of the apparatus of FIG. 2;

FIG. 4 is an enlarged fragmentary view of a portion of the apparatus of FIGS. 2 and 3 as seen from the bottom and represented as cut by a broken plane 4--4 indicated in FIG. 3;

FIG. 5 is a fluid circuit diagram illustrating the fluid flow of the apparatus; and

FIG. 6 is an electrical circuit diagram of the apparatus.

Like characters are utilized throughout the drawing to designate like parts .


As shown in FIG. 1, a fluid circulating, heating and temperature control unit 11 is provided for connection to a thermal blanket or heating pad 12 having fluid circulating ducts therein connected to the unit 11 through an inlet tube 13 and an outlet tube 14. The unit 11 comprises a flanged bulkhead 15, shown in FIGS. 2 and 3, upon which most of the parts are mounted, a reservoir 16 for a suitable fluid such as water and a cover or hood 17 to form a unitary integral closed structure. The reservoir 16 is secured to the lower surface of the bulkhead 15 and the cover 17 is secured to the flange 18 of the bulkhead 15. The cover 17 is provided also with a handle 19 for carrying the unit, rendering it readily portable.

The bulkhead 15 has suitable openings for mounting a fluid heater 21, a drive motor and pump assembly 22, a filler spout 23 and a fluid temperature sensor block 24. As shown, the motor pump assembly 22 comprises an electric motor 25 directly coupled to a fluid circulator 26 in the form of a centrifugal pump. The common motor-pump shaft 27 also carries an air circulator or fan 28. It will be understood that suitable shaft packing is provided to prevent water from the pump 26 or the reservoir 16 from entering the motor 25.

The heater 21 comprises a mounting plate 31 carrying an immersion type electrical resistance heater 32 projecting downward into the reservoir 16 and terminals 33 and 34 above the bulkhead 15 for making electrical connections.

As illustrated in FIG. 2, the cover 17 is formed with a recessed portion 35 to provide access to the filler spout 23 without removing the cover 17. The filler spout 23 is formed with a reduced diameter threaded nipple portion 36 with suitable means such as a knurled nut 37 and gasket 38 for non-leakably securing it in the bulkhead 15. A threaded filler cap 39 is also provided.

The sensor 24 is in the form of a block in which two channels 48 and 49 are formed, each substantially in the form of an elbow as illustrated in FIGS. 2 and 3. One channel 48 forms a connection between the pump outlet port 41 through tubing 42 to a reservoir outlet port 43. The other channel 49 in the sensor block 24 provides a connection between a reservoir inlet port 44 and a passageway through tubing 45 into the reservoir 16. The pump 26, tubing 42, and the channel in the sensor block 24 connected thereto form a portion of a passageway from the fluid in the reservoir 16 at the pump inlet port 46 to the reservoir outlet port 43 (FIG. 4).

Thus, a fluid circuit is provided from the pump inlet 46 through the pump 26, the pump outlet port 41, the tubing passageway 42, one channel 48 in the sensor block 24, the reservoir outlet port 43, heating pad inlet tubing 13, the pad 12, pad outlet tubing 14, the reservoir inlet port 44, and the second channel 49 in the sensor block 24 with a return passageway into the interior of the reservoir 16 through the tubing 45.

In order to obtain better and more satisfactory control of the actual temperature affecting the user of the pad 12, the control is made responsive to the temperatures of both the inflow into the pad 12 and the outflow therefrom instead of merely to one or the other of these temperatures or the temperature of the fluid within the reservoir 16. This is accomplished by providing a thermostat 47 subjected to the temperature of the sensor block 24.

The thermostat 47 is mounted upon the sensor block 24 with the block 24 in heat conducting relationship to the thermostat 47 so that the thermostat responds to both the inflowing and outflowing temperature of the pad 12 of the fluid flowing through the channels 48 and 49 in the sensor block 24, acting substantially in accordance with the average temperature. The thermostat 47 is mounted in thermal relationship to the sensor block 24 by means of a bracket 51 which is integral with or clamped directly against the block 24. The block 24 and the bracket 51 are composed of suitable high heat conductivity material such as brass or copper. Moreover, the block 24 is large enough so that it has large mass compared to the thermostat 47, and its thermal or heat storing capacity is large in relation to the thermostat 47. Consequently, fluctuations in ambient temperature have relatively little effect on the temperature control unless fluid temperature is varied.

The thermostat 47 is shown being of the bi-metallic type, having a bi-metal strip 52 carrying an electrical contact 53 cooperating with a flexible blade contact 54. The bi-metal strip 52 and the blade contact 54 are connected to electrical circuit conductors 55 and 56, respectively.

In order that the controlled temperature may be adjusted, the thermostat blade contact 54 is made flexible and adjustable in position. Means are provided for adjusting the position which may take the form, for example, of a threaded pin 57 having a tip 58 bearing against the contact blade 54. Means are provided for biasing the blade 54 in a position toward the pin 57, which may take a form for example of a button of insulating material 59 carried by a metal strip 61. It will be understood that the electrical contact members 52 and 54 are electrically separated from each other and from the supporting bracket 51 by a suitable means such as blocks 50 composed of a material which is electrically insulating but which conducts heat.

Inlet louvers 62 and outlet louvers 63 are provided in the cover 17 in order that the fan blades 28 may produce air flow in the direction of the arrows 64 around the fan 28 from the thermostat 47 and the sensor block 24 toward the heater 21 in order that the sensor 24 will not be affected directly by the heat produced by the heater 21. The recessed portion 35 of the cover 17 serves not only for providing access for the filler spout 23 but also as a baffle to direct the flow of air along the arrows 64, so that the air is caused to enter through the louvers 62 and leave through the louvers 63 and to travel in a desired direction with respect to the sensor 24 and the heater 21.

A temperature limit thermostat 65 is provided for safety in the event that the blockage of any of the passageways or leakage of fluid from the pad 12 or elsewhere in the system should interrupt the flow of heated fluid through the channels 48 and 49 of the sensor 24 so as to interfere with the operation of the thermostat 47 in cutting off the heater 21.

The temperature limit thermostat 65, shown in FIG. 6, comprises a bi-metal contact member 66 and a blade contact member 67 which are so mounted, in electrically insulating relation but thermal conducting relationship to a probe 70 extending into the reservoir 16, as to separate the contact members 66 and 67 whenever the temperature of the fluid in the reservoir 16, exceeds a predetermined value. This value is selected to be somewhat higher than the maximum temperature setting of the adjustable thermostat 47. It will be apparent that the probe 70 will become overheated so as to open the contacts of the temperature limit thermostat 65 whenever the fluid such as water or, in the event of leakage from the reservoir 16, air in the reservoir 16 reaches an excessive temperature.

As shown in FIGS. 2 and 6, the thermostats 65 and 47 are connected in series with the heater coil 32 to input lines 68 and 69 from electrical input terminals 71 adapted to be connected to a source of electrical current such as the central station lighting system. Thus an electrical circuit is formed from the line 68 through a conductor 72, the heater coil 32, a conductor 73, the contact members 67 and 66 of the temperature limit thermostat 65, a conductor 74, the conductor 55, thermostat 47, the conductor 56, conductors 79 and 81 and switch contacts 75 of a switch 76, back to the input line 69. A parallel electrical circuit for the pump and fan driving motor 25 is provided from the input terminals 71 through the conductor 68, a conductor 78, the motor 25, conductors 77 and 81, and the switch contact 75 back to the current supply line 69.

Preferably, check valves 83 and 84 are provided in the fittings forming the inlet and outlet ports 43 and 44 of the reservoir 16. Likewise connectors 85 and 86 are preferably provided at the ends of the hose lines 13 and 14 to the pad 12 which contain check valves 88 and 89, respectively. In this manner the heating and temperature control unit 11 may be disconnected from the pad 12 without loss of fluid from either of them. As illustrated in FIG. 4, each of the connectors 85 and 86 is provided with a threaded sleeve cooperating with the mating thread on the fitting of the reservoir 16 so that fluid tight connections may be made.

In order that the check valves will be open when the connectors have been threaded onto the fittings in the position shown for the fitting 84 in FIG. 4, one set of check valves for example the check valves 88 and 89 of the hose connectors are provided with depressor pins 92 and 93. The pins 92 and 93 are of the length that when the connection is made both check valves such as the ball check valve 94 in the reservoir inlet fitting 44 and the cone check valve 95 in the connector 86 are moved away from their seats, against the force of biasing springs 96 and 97. However, when the parts are disconnected, as shown for the outlet fitting 43 and the connector 85, the springs press the ball check valve 83 and the cone check valve 88, respectively, against their seats so as to close the openings and prevent leakage of fluid. This permits the apparatus to be carried about without loss of fluid or spillage.

As illustrated in FIG. 1, the heating pad 12 comprises two sheets of flexible, fluid-impervious material such as rubber or synthetic sheet with edges 98 heat sealed and a plurality of straight and right-angle lines heat sealed to form parallel ducts extending from the inlet hose 13 to the outlet hose 14. A right angled heat sealed line 101 separates inlet ducts from outlet ducts. A heat sealed line 102 divided the inlet area into two inlet ducts. The inlet ducts are left open at the ends of the heat sealed lines 101 and 102 at 103 and 104 to permit the circulating fluid to divide and travel in parallel ducts 105, 106, 107, 108, 109, 110-123, formed by straight heat sealed lines 124, 125, 126 for example, and right angle lines 127, 128 and 129, for example.

In this manner a plurality of parallel passageways or ducts are provided. Near the inlet ends of the ducts the flow in the ducts near the edge of the pad is in longer paths but near the outlet end the flow is in shorter paths. In this manner the lengths of the various parallel paths of flow are substantially equalized. Consequently, substantial equalization of the amount of flow in the various ducts takes place and the heating effect of the fluid is well distributed. It is unnecessary to provide a single long circuitous path for the fluid in order to obtain equalization of the fluid throughout the pad. The use of the parallel ducts provides considerably less resistance to flow of fluid and enables adequate rates of flow to take place although a very small pump motor 25 is required.

A specific embodiment of the invention has been illustrated and described by way of illustration, but it will be understood that the invention is not limited to the specific arrangements disclosed and comprehends modifications falling within the scope of the invention.