US1935120A - Fan - Google Patents

Description

Nov. 14, 1933. H F, HAGEN 1,935,120

FAN

Filed Oct. 31, 1929 2 Sheets-Sheet l ZTraR/VEY Nov 14, 1933.

H. F. HAGEN FAN Filed Oct. 31, 1929 2 Sheets-Sheet 2 F/GZ /NVENTO/? M 1 f Arm/ways Patented Nov. 14, 1933 UNITED STATES FAN Harold F. Hagen, Dedham, Mass., assignor to B. F. Sturtevant Company, Hyde Park, Mass., a corporation of Massachusetts Application October 31, 1929. Serial No. 406,752

Claims.

The present invention relates to fans.

During periods of light load, mechanical draft fans are frequently shut down to permit operation of the boilers on the stack draft alone. When I 5 the fans are thus shut down, care must be exercised to make sure that the stack passages are unimpeded, otherwise severe damage-is likely to result. output controlling devices, such as throttling means, in earlier constructions, or spin controlling devices of the type described in my co-pending application Serial No. 210,666, filed August 4, 1927, an additional burden is placed on the operator to open the passage during periods of stack l5 draft operation.

It is evident, however, that serious consequences may follow in the event of neglect on the part of the operator.

The object of the present invention is to pro- ,20 vide automatic means for insuring an unimpeded draft passage for the flue gases whenever a fan is shut down to permit operation on the stack draft alone.

With this object in view, the principal feature of the invention comprises by-pass means connecting the inlet and outlet of the fan adapted to be normally inoperative during operation of the fan but constructed and arranged to open the passage upon shutting down of the fan. In

" its simplest form, the invention comprises a counter-balanced by-pass damper adapted to be actuated by the difference in pressure existing between the inlet and outlet of the fan upon the decrease in pressure in the fan'outlet brought -85 about by operation of plant on the stack draft.

Other features of the invention consist in certain novel features of construction, combinations and arrangement of parts hereinafter described and particularly defined in the claims. In the accompanying drawings, Fig. 1 is a side elevation of the preferred form of induced draft fan and inlet and outlet connections embodying the features of the presentinventidn; Fig. 2 is a front elevation .of the fan shown in Fig. 1; and

Fig. S-is a fragmentary detail in section onan Inasmuch as fans are often provided with During normal operation of the fan, the vanes are adjusted to any desired inclination to control the amount of flue gases handled by the fan. At the lightest load which the fan can handle at a given speed, the vanes are entirely closed, the spin velocity being then a maximum and the gas being passed entirely through leakage spaces between the vanes. For even lighter loads, the fan is shut down and the stack draft is availed of to operate the plant.

Inasmuch as the stack draft alone is insufficient to create any appreciable current of air through the vanes when closed, provision is made for lay-passing the flue gases directly from the inlets to the outlet. According to this construction, the plates 14 which are common both to the inlet scrolls and the outlet, are provided with bypass openings 16. A swinging damper 18 is adapted normally to close each opening. The

damper is adapted to swing inwardly as shown in Fig. 2, that is to say, into the outlet, upon a diminution of outlet pressure below the pressure existingin the inlet.

Each damper normally closes against a flange 20 secured to the plate 14 around-the opening. 30 The damper is provided with ears 22 which are secured to a shaft 24 journaled in bearings 26 and 28. The bearing 26 is attached to the inner side of the plate 14 and the bearing 28 is mounted on, an angle iron 30 secured to the periphery 5 of the outlet box. v The shaft is counter-weighted by means of an arm 32 carrying a ball 34. The counter-weight is nicely adjusted so that upon the slightest increase in pressure in the inlet over the outlet, the damper swings open. The 99 damper is limited in its opening movement by a pair of stops 36 and 38 secured to arcuate-brack- .ets 40 which are attached to the plate 14 at 42.

, During normal operation of the fan, the pressure in the outlet is somewhat greater than the pressure in the inlet. The damper therefore remains closed and in no way interferes with the mechanical draft. The damper remains closed for-all positions of the vanes 12 even when the latter are in fully closed position, provided only 1 Bit are open when the fan is shut down. It is immaterial whether the vanes are opened or not. If the vanes are opened, the difference in pressure between the inlet and outlet may not be sufllcient to open the damper but in such case, opening of the damper is unnecessary because a suflicient unimpeded passage is afforded through the fan itself. However, if the vanes are closed, the pressure diiference between the inlet and outlet opens the damper and thus assures an unimpeded passage of air through the by-pass. The damper mechanism therefore operates automatically to avoid the consequence of careless operation.

It will be obvious that although the invention has been described as embodied in a construction employing spin controlling vanes for varying the output of the fan, such particular output controlling means is not essential, and the invention may be embodied in other constructions employing any type of output control such, for example, as throttling means.

Having thus described the invention, what is claimed is:

1. A centrifugal fan having a rotor and a casing comprising an outlet scroll and an inlet scroll at the side thereof with a partition between, the partition being provided with a by-pass opening, devices in the inlet scroll for controlling the flow of fluid from the inlet to the rotor, and means normally closing the opening and opening automatically when the flow of fluid through the rotor reaches a predetermined'minimum.

2. An induced draft fan adapted to receive fluid and deliver it to a stack comprising a rotor, an outlet adapted to be connected to the stack, an inlet adapted to be connected to the source of the fluid, devices for controlling the delivery of fluid to the rotor, and normally closed by-pass me between the inlet and outlet operating automatically by the suction produced by the stack for opening said means when the rotor is out of operation and said devices prevent the flow of fluid through the rotor.

3. The combination with a fan having an inlet, an outlet, a rotor, and output controlling means for varying the passage of fluid through the rotor from inlet to outlet and having provision for substantially impeding the passage of fluid when the rotor is stationary, of means operated automatically by a decrease of pressure in the outlet below that in the inlet to by-pass fluid around the output controlling means.

4. The combination with a fan having an inlet, an outlet, a rotor, and output controlling means for varying the passage of fluid through the rotor from inlet to outlet and having provision for substantially impeding the passage of fluid when the rotor is stationary, of by-pass means around the output controlling means, and a pressure operated damper in the by-pass means to open by a drop in pressure in the outlet below that in the inlet, occasioned by stopping the rotor with said output controlling means in closed position.

5. The combination with a mechanical draft fan having an inlet, an outlet, and a rotor, and adapted to be connected to a stack to subject the outlet to a suction by stack draft, of output controlling means to vary the passage of air through the fan when .the rotor is running and adapted when closed to substantially impede passage of air with the rotor stationary, and a by-pass damper normally closed and operated by the stack suction to permit direct passage of air from the lid inlet to the outlet on impeding the passage through the rotor.

F. HAGEN.

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