Leaking Valves

Cylinders with leaking or defective valves should be tagged as such and turned in to the nearest naval supply depot for overhaul.

Pressure Control

The pressures of the various cylinder gases must be reduced to a suitable working pressure before they can be safely used. Pressure is reduced by a regulator or reducing valve which controls the flow of gas from the cylinder. Regulators are the single-stage type, which reduces gas pressure in one step, or the double-stage type, which reduces pressure in two steps or stages.

Safety Precautions

Cylinders, regulators, hoses, and torches are important parts of the shop equipment for

heating, welding, and cutting. Learn and follow these safety rules for this type of equipment.

1. Never fill a cylinder with a gas other than the gas for which it is specifically designated. Never remove or change the decals.

2. Never return an empty cylinder without making sure that valves are closed and that protective caps are in place.

3. Never drop the cylinders or let them strike against each other.

4. Never use cylinders as rollers or supports.

5. Never hammer or strike the valve wheel to open or close the valve. Use only the wrenches or tools approved for that purpose.

6. If valve outlets are iced, use only warm water to free them. Never use hot or boiling water.

7. Never use a cylinder that is improperly marked; that is, where the paint color doesn't agree with the information on the decal.

8. Never use a lifting magnet or a sling to raise or handle a cylinder.

9. Be careful not to mix full and empty cylinders in a stowage rack.

10. Never tamper with safety devices on the valves or cylinders.

11. Never store oxygen and acetylene cylinders in the same immediate area.

12. Be especially careful that you never strike an arc on gas cylinders or sealed metal cylinders of any kind.

13. Acetylene and low-pressure fuel-gas cylinders, which have been stowed in a horizontal position, must be placed in a vertical position for at least 2 hours before you use them. This will allow the porous filler material inside the cylinder to settle.

MAINTENANCE AND REPAIR OF VALVES

Periodic maintenance is the best way to extend the service life of valves and fittings. As soon as you see a leak, check to see what is causing it; then apply the proper remedy. This remedy may be as simple as tightening a packing gland nut. A leaking flange joint may need only to have the bolts tightened or to have a new gasket inserted. Dirt and scale, if allowed to collect, can cause leakage. Loose hangers permit sections of a line to sag. The weight of the pipe and the fluid in these sagging sections may strain joints to the point of leakage.

Whenever you are going to install a valve, make sure that you know its function. In other words, is it supposed to prevent backflow, start flow, stop flow, regulate flow, or regulate pressure? Look for the information that is stamped on the valve body by the manufacturer: type of system (oil, water, gas); operating pressure; direction of flow; and other information.

You should also know the operating characteristics of the valve, the type of metal it is made of, and the type of end connection it has. Operating characteristics and material affect the length and kind of service that a valve will give. End connections indicate whether or not a particular valve is suited for installation in the system.

Valves should be installed in accessible places, and with enough headroom to allow for full operation. Install valves with stems pointing upward, if possible. A stem position between straight up and horizontal is acceptable, but avoid the inverted position (stem pointing downward). When the valve is installed in the latter position, sediment will collect in the bonnet and score the stem. When a line is subject to freezing temperatures, liquid trapped in the valve bonnet may freeze and rupture it.

Globe valves may be installed with pressure either above or below the disk. It will depend upon which method will be best for the operation, protection, maintenance, and repair of the machinery. You should ask what would happen if the disk became detached from the stem? It is a major consideration in determining whether pressure should be above the disk or below it. Check the blueprints for the system to see which way the valve must be installed. Pressure on the wrong side of the disk can cause very serious damage.

Valves which have been in constant service over a long period of time will eventually require gland tightening, replacing, or a complete overhaul of all parts. If a valve is not doing the job, it should be dismantled and all parts inspected. All defective parts must be repaired or replaced.

GLOBE VALVES

The repair of glove valves (other than routine renewal of packing) is generally limited to refinishing the seat and disk surfaces. You should take the precautions described below when you do this work.

When refinishing the valve seat, remove no more material than is necessary. Valves that do not have replaceable valve seats can be refinished only a limited number of times.

Before you begin any repair work on the seat and disk, check the disk to make certain it is secured rigidly to, and is square on, the valve stem. Also, check to be sure the stem is straight. If the stem is not straight, the disk cannot seat properly. Inspect the seat and disk carefully for evidence of wear, for cuts on the seating area, and for improper fit of the disk to the seat. If the disk and the seat appear to be all right, they should be spotted-into find out whether they actually are in good condition.

Spotting-in Valves

Spotting-in is the method used to determine visually whether or not the seat and the disk make good contact with each other. To spot-in a valve seat, first apply a thin coating of prussian blue evenly over the entire machined face surface of the disk. Then insert the disk into the valve and rotate it a quarter turn, using a light downward pressure. The prussian blue will adhere to the valve seat at those points where the disk makes contact. Figure 5-54 shows what correct and imperfect seals look like when they are spotted-in.

After you have examined the seat surface, wipe all the prussian blue off the disk face surface. Apply a thin, even coat of blue to the contact face of the seat. Again, place the disk on the seat and rotate the disk a quarter of a

Figure 5-54.-Examples of spotted-in valve seats.

turn. Examine the blue ring that appears on the disk. It should be unbroken and of uniform width. If the blue ring is broken in any way, the disk is not making a proper fit.

Grinding-in Valves

Grinding-in is the manual process used to remove small irregularities by grinding together the contact surfaces of the seat and disk. Grinding-in should not be confused with refacing processes in which lathes, valve reseating machines, or power grinders are used to recondition the seating surfaces.

To grind-in a valve, first apply a small amount of grinding compound to the face of the disk. Then insert the disk into the valve and rotate the disk back and forth about a quarter of a a turn. Shift the disk-seat relation from time to time so that the disk will be moved gradually, in increments, through several rotations. During the grinding-in process, the grinding compound will gradually be displaced from between the seat and disk surfaces. Therefore, it is necessary to stop every minute or so to replenish the compound. When you do this, wipe both the seat and the disk clean before applying the new compound to the disk face.

When it appears that the irregularities have been removed, check your work by spotting-in the disk to the seat in the manner previously described.

Grinding-in is also used to follow up all machining work on valve seats or disks. When the seat and disk are first spotted-in after they have been machined, the seat contact will be very narrow and will be located close to the bore. The grinding-in, using finer and finer compounds as the work progresses, causes the seat contact to become broader. The contact area should be a perfect ring covering approximately one-third of the seating surface.

Be careful that you do not overgrind a seat or disk. Overgrinding tends to produce a groove in the seating surface of the disk. It may also round off the straight, angular surface of the disk. Overgrinding must be corrected by machining.