TYPES OF FIRE APPARATUS PUMPS THAT ARE POPULAR IN EUROPE
Pumpers Now Regarded as a Necessary Part of the Fire-Fighting Equipment—Types of the Pumps Installed on These Apparatus
THE following is interesting as showing the European point of view in regard to the motor fire pumper and the type of pump best suited for this apparatus:
Although the motor pumper was not adopted with great rapidity in European cities, it is now of course regarded as a necessary part of modern fire-fighting equipment. Moreover the actual pump is essentially a job for the centrifugal pump designer and builder and at least two well known builders of these pumps have turned their attention to the requirements of fire-fighting.
Advantages of the Centrifugal Pump
There are many reasons why the centrifugal pump is superior in this application to any form of reciprocating pump. In the first place, the power unit is a high speed engine and this type of pump being essentially a high speed pump can be driven when required direct by the engine. Water is delivered by a centrifugal pump in a steady uniform stream entirely free from shock eliminating a good deal of wear on the hose while as dangerous rises of pressure cannot be developed safety devices on the delivery are unnecessary. Changes can therefore be made in the hose while the pump is running, while it is hardly necessary to point out the centrifugal pump will handle dirty and gritty water without any appreciable damage, or only damage to such parts as are easily renewed. For its output the centrifugal pump can be designed to occupy the minimum space and is a consistently reliable machine, although to ensure full delivery being rapidly reached an efficient priming pump must form part of the equipment.
Special Requirements for Motor Pumpers
The modern motor pumper demands something more than the mere fitting of a stock pattern centrifugal pump to an extension of the engine shaft. In the first place in cold climates freezing must be guarded against by water jackctting the pump and circulating the engine cooling water around it Then again arrangements are made in the shape of a by-pass between suction and pressure branches. This connection is made use of when the pump is fed from a hydrant at low pressure. In such cases with sufficient pressure at the hydrant the pump is out of action and the water passes through the open by pass, but should water at high pressure be wanted it is a simple matter to close the by-pass thus enabling a quick change over to be made without any interference with the hose.
Sulzer Fire Pumps
As centrifugal and turbine pumps of this design are well known it is not surprising to find the firm’s fire pumps with novel features coupled with a high overall efficiency. A section of the latest design is shown in Fig. 1. It is capable of conforming to the varied requirements of a fire pump by being arranged for delivering small quantities of water at high pressure and large quantities at correspondingly lower pressure, this being arranged for by running the impellers in series or in parallel as the case may be. The change over can be effected while the pump is working and irrespective of its speed or the power of the motor. It is all done by a simple valve. The arrangement is designed so that it is fool-proof. In Fig. 1 the impellers are assumed to be working in parallel. The suction chambers a a’ of the two impeller pairs are connected to each other, similarly the two pressure chambers c and d are connected by means of passage b; passage e being closed. With the valve in this position the pump delivers double the quantity of water at half the pressure. In order to put the impeller in series the two suction chambers a a’ are disconnected from each other, the passage b is closed cutting off the connection between the two pressure chambers c and d and the passage e is opened. With the valve in this postion the pump delivers half the quantity of water at double the pressure. The suction chambers it will be observed are in the center of the pump, and arrangement which causes the two end stuffing boxes to be under pressure. As a general rule stuffing boxes under pressure are well avoided in centrifugal pumps, but in this particular application the arrangement may be regarded as beneficial inasmuch as ingress of air is absolutely prevented.
This change over device is of considerable advantage in fire-fighting because not only does the pump permit of its adaptation to a wide variation in the fire stream, but the low pressure arrangement makes it very useful for pumping out cellars and other flooded areas while on board ship the dual application of a low pressure deck washing pump and a high pressure fire pump when required is one which will appeal to marine engineers.