It is important to study the construction of this valve, illustrated and described. If the generator is of a portable type the hydraulic valve will be attached to it (Fig. 53). If it is of a fixed type the hydraulic valve is usually separate, and should be fixed with iron tubing of suitable size connecting it with the generator gas outlet.

Cutting Blowpipe

After blowing through the tubing as described, one end should be fixed to the oxygen coupling O (Fig. 49) of the cutting blowpipe, and the other end fixed to the regulator outlet C. (It is assumed that the construction of the cutting blowpipe already illustrated and described has been already examined.)

The flexible tubing for coupling the hydraulic valve acetylene outlet tap B (Fig. 54) to the acetylene branch tap H of the cutting blowpipe (Fig. 49) should now be attached. This tubing is not subject to a greater pressure than that due to the bell of the acetylene holder of the generator, so that ordinary good quality rubber tubing is suitable for this purpose, but as it is usually liable to be subjected to rough usage, it is a wise precaution to employ similar tubing to that used for oxygen. Before coupling the tubing up, however, it is desirable to blow it through by any suitable means (preferably not an oxygen cylinder) to make sure that it is clear and free from dust.

The cutting guide A (Fig. 49) which may consist of the ordinary standard spade guide, or a roller guide, should also be fixed to the nozzle and adjusted so that the nozzle will be the correct distance away from the plate when cutting (refer forward to pages 91 to 93.

Acetylene Generator

Before the generator is put into operation the hydraulic back pressure valve must be filled with water in accordance with directions already given. This is a precaution of the utmost importance, and subsequently, at least once a day, and always after any displacement of water by back fire, this valve should be replenished in the manner indicated. The generator should now be charged with carbide, but before doing so it is very important to read carefully the maker's printed instructions, and study the Regulations and Precautions previously given.

Before Starting Up It Is Necessary

1. To clear all air from generator spaces and acetylene piping, see that the oxygen cylinder valve is closed and all traps on the acetylene line between the generator and the cutting blowpipe nozzle are open. Then start the generator to produce acetylene in accordance with the maker's instructions. It will soon be found that gas is being emitted from the cutting blowpipe nozzle. This will at first be air. When it begins to smell strongly of acetylene, light the gas, and when it is obvious that all the air has been displaced, close the acetylene tap H on the cutting blowpipe (Fig. 49 and 50). The generator will continue to produce acetylene and raise the bell of the holder until it is automatically shut off.

2. See that passages of the cutting blowpipe are clear. The outlet tap on the regulator must be open, also the valves R and G (heating and cutting oxygen) on the cutting blowpipe. Then slowly open the cylinder valve by tapping the extended lever key with the hand. By this means all the oxygen passages of the cutting blowpipe will be cleared and oxygen will blow off at the nozzle.

Having thus ascertained that the passages of the cutting blowpipe are clear, completely close the valves G and Ft so that no oxygen is flowing through the blowpipe nozzle.

The cylinder valve may then be fully opened, for which purpose one complete turn of the spindle is usually ample. Subsequently,when oxygen has to be shut off from the cutting blowpipe whilst work is in progress, the regulator outlet tap should be used for the purpose, but always shut the cylinder valve when the work is finished, or when cylinder is empty.

The Complete Apparatus is now ready for use.

Having connected up the various units and started the generator, we are ready to start cutting ; therefore, assuming that the nozzle in the blowpipe is the correct size for the work in hand, the first thing to do is :-

1. ;Adjust the Regulator to the correct pressure (refer also to page 93).-This must always be done with the cutting oxygen valve open ; therefore, open the valve G on the blowpipe, Figs. 49 and 50 (tap H and valve R remaining closed), and, while the oxygen for cutting is escaping, quickly adjust the screw A on the regulator, Fig. 52, until the low pressure gauge L records the pressure required. Immediately close the valve G. We may now-

2. ;Light the Cutting Blowpipe.- All valves on the cutter are at present closed. Partially open the valve R, allowing a gentle stream of oxygen to pass through the heating nozzle ; now, slowly open the acetylene tap H on the blowpipe. Mixed gases will now be passing through the nozzle. A light should be applied to the nozzle, and, when alight, the heating flame must be adjusted to the required conditions by regulating the tap H and the valve R.

Note

For cutting steel, the correct oxy-acetylene flame should have a white cone 1/8 in. to 3/8 in. long, according to the thickness of work, extending beyond the nozzle. For cutting cast iron the cone may have to be about 3Jin. long. See also page 420 and Fig. 221.

3. ;Heat the Edge of the Plate to be cut.-The flame thus adjusted may now be applied to edge of the plate to be cut. While doing this, press down the thumb lever P, and at the same time unscrew the valve G ; press down the thumb lever P all the time the plate is being heated, and continue to heat until the part where the cutting has to commence is incandescent.

4. ;Cutting.-When the incandescent state is reached, release the thumb lever P and commence to cut by moving the cutter with a steady movement across the plate where it is desired to cut. If, when the cut is finished, another cut is to be started immediately, the cutting oxygen is shut off by merely pressing down the thumb lever.

But if some time is to elapse, or the work has to be readjusted, before starting another cut, the valve G should be screwed down. The advantage of the hand or thumb lever P will very soon become obvious to the operator.

When cutting has been completed or when it is desired to stop work, the acetylene tap H should always be shut off first ; then the oxygen valves R and G. If the work is stopped for any considerable time the oxygen cylinder valve and also the acetylene taps A and B on the hydraulic valve should be closed. When recommencing work see that all the foregoing Instructions and Precautions are complied with.

Glasses (preferably smoked) should always be used to protect the eyes of the operator from particles of burnt metal.

It is desirable also to take suitable precautions to protect the clothes.

Practical experience is necessary, and practical instruction desirable before cutting can be done efficiently, but there is no reason why anyone who has read the foregoing instructions should not obtain passably good cutting after a little practice.