Hydrauliska Kompressorn

The Hydraulic Compressor in Persberg

Background

The hydraulic compressor was built starting in 1911 because of the limited availability of power at the mining field. The 300 horsepower available through the agreement with Älvestorp Ironworks Company was no longer sufficient.

By replacing the existing electrically driven compressor with a hydraulic compressor, about 175 hp were freed for other uses, including new hoisting engines in the mining field.

Location and Construction

The compressor was built above the abandoned Krangruve Shaft, which was 56 metres deep, northwest of Krangruvan.

From the 106-metre level, a raise was driven upward to connect with the shaft from a blasted chamber that served as an air reservoir.

Water Supply

The compressor was powered by water from the Persberg canal, which was available because most of the water-driven pumping and hoisting wheels had been taken out of service.

Water reached the compressor from the intake dam through a 420-metre wooden pipe with a diameter of 1050 mm.

The system was designed for a flow of 900 litres per second, but only about 600 l/s could be delivered due to the limited capacity of the canal.

The minimum flow required during operation was about 450 l/s. At flows below 300 l/s, the water could no longer carry the air down to the air chamber.

The Suction Head

Figure 3 shows the movable suction head, where air and water were mixed.

Water flowed through 49 pipes with an internal diameter of 109 mm. Inside each of these hung seven smaller pipes with an internal diameter of 23 mm, whose upper ends were above the water surface.

The height of the suction head relative to the water level could be adjusted to achieve maximum efficiency.

As water flowed through the larger pipes, air was drawn in through the smaller pipes. The air-water mixture was carried down to the air reservoir, where it struck a cone that spread the mixture outward.

Here the air and water separated. The water was then forced back up to the surface by the air pressure and flowed out into Lake Yngen.

Contemporary Description

In “Technical Association of Örebro 1875–1925: Commemorative Publication” the compressor is described as follows:

“In 1915 the first and so far the only compressor of its kind in Sweden was built in Persberg, a so-called hydraulic compressor. Air is drawn in by falling water, and the air bubbles are compressed by the increasing pressure of the water.”

A Memory from the 1950s

Olle Pettersson of Persberg (born 1935) recalled a repair he carried out on the compressor in the late 1950s.

In addition to the water separation in the air chamber, there was also an extra water separator containing a float that controlled a valve.

The float was made from 3 mm copper plate, formed into two hemispheres that had been soldered together. When it began to leak, Olle was tasked with repairing it.

The soldering proved difficult. If he heated it too much, air blew out and blew the solder away; if he heated it too little, the solder was drawn inward.

He solved the problem by drilling a small pressure-equalizing hole, threading it, and sealing it with a screw and gasket.

Olle began working at the mine in 1953 in the mechanical department and later also supervised the mechanical training of students at the mining school.