Page:Walker (1888) The Severn Tunnel.djvu/68

Rh ‘H-piece,’ and the top valve up the main column of  the pump and out to the required level.

The plunger is much the better pump for continuous work, as any slight wear there may be upon the pole itself is easily made good by packing the stuffing-box, while the faces of the buckets in the bucket-pumps are continually wearing by friction against the sides of the working barrel. (The drawings of the large pumps and engines at Sudbrook, given at the end of this volume, will show the difference between the bucket and the plunger-pump.) Of course we should have preferred that all the pumps should have been plungers, but it is necessary in fixing a plunger-pump to get to the bottom of the pump to fix the pole-case as well as the bottom of the rising main securely, and after it is at work to pack the stuffing-boxes. It was impossible to put down plunger-pumps while the shafts were full of water, and it was for this reason that, in the first place, bucket-pumps were adopted and ordered.

The engines for working the pumps were of two sorts, beam-engines and Bull-engines—the latter being so called after the inventor. Both engines take steam only at one end of the cylinder.

The beam-engine takes steam only above the piston. The pressure of the steam when admitted forces down the piston, pulls down the inner end of the beam to the full extent of the stroke, raising the outer end of the beam which carries the pump-rods, and thus making the up-stroke of the pump.