Repacking Valve Stuffing Boxes
If the stem of a globe valve is in good condition, stuffing box leaks can usually be stopped by setting up on the gland. If this does not stop the leakage, repack the stuffing box. The gland must not be set up or packed so tightly that the stem binds. If the leak persists, a bent or scored valve stem may be the cause of the trouble.
Coils (string) and rings are the common forms of packing used in valves. The form to be used in a particular valve will be determined, in part, by the size of the packing required. In general, rings are used in valves that require packing larger than onefourth inch. When a smaller size is required, string packing is generally used.
When you repack a valve stuffing box, place successive turns of the packing material around
the valve stem. When strong packing is used, coil it around the valve stem. Bevel off the ends to make a smooth seating for the bottom of the gland. Then put on the gland and set it up by tightening the bonnet nut or the gland bolts and nuts. To prevent the strong packing from folding back when the gland is tightened, wind the packing in the direction in which the gland nut is to be turned. Usually, where successive rings are used, the gaps in the different rings should be staggered.
Gate, globe, angle, and stop check valves are made to back seat the stem against the valve bonnet when the valve is fully opened. Back seating of these valves is a safety feature to eliminate the possibility of the stem being forced out under pressure while the valve is fully opened. Back seating makes possible the repacking of the stem stuffing box under pressure. However, you should attempt this only in emergencies and with extreme caution.
The manner in which a gate valve is used has a great deal to do with its service life. Gate valves should always be used either wide open or fully closed; never in a partially opened position. When a gate valve is partly open, the gate is not held securely, but swings back and forth with the pulsation of the flow. As the gate swings, it strikes the valve body and the finished surfaces, nicking and scoring them. When these surfaces are imperfect, the valve gate cannot set accurately and seal off the flow. A gate valve should never be installed in any position where a throttling or flow-regulating valve is required. A globe valve should be used in those situations,
Lapping is the best way to correct gate valve defects such as light pitting or scoring and imperfect seat contact. The lapping process is basically the same for gate valves as it is for globe valves. The exception is that the lapis turned by a handle which extends through the end of the valve body. Remove the valve from the system. Insert the lapping tool, without its handle, into the valve so that it covers one of the seat rings. Then attach the handle to the lap and begin the lapping. The wedge gate can be lapped to a true surface, using the same lap that is used on the seat rings. (CAUTION: DO NOT use the gate as a lap.)
Do not remove any more material than is necessary. You can resurface a gate valve only a limited number of times. By removing too much material you will reduce the number of times the surface can be refinished, and the life of the valve.
Leakage around the stem of a gate valve is caused by troubles similar to those in leaking globe valves. The same procedure is used to stop these leaks in both valves.
Leaks are the principal trouble found in check valves. Leakage is caused by a pitted disk or valve seat. Pitting is usually caused by abrasives caught between the disk and the seat.
When a check valve requires maintenance because of pitting, the work will depend upon the type of disk in the valve. With a ball-type disk, you will have to replace the ball and grind the seat. A flat or conical disk, can be repaired by grindingin the disk to its seat with a fine grinding compound.
Remember that fluid will flow through them in only one direction, Be sure that they are installed correctly.
The weapons department personnel test and care for the hydraulic control valves in magazine sprinkling systems. However, DCs will handle leaks and other failures in these valves.
Most leaks in these valves are caused by a failure of the leather disk insert. The flow of water tends to force these inserts to curl up over the valve seat. When that happens, the valve is not completely tight when it closes. These leather inserts should be replaced with a rubber disk as soon as possible.
Other troubles with these valves include leakage of hydraulic oil past the piston of the main control valve, a broken closing spring, leakage of hydraulic oil through the upper packing gland, or leakage of water through the lower packing gland.
You may see a loss of hydraulic power after the valve opens or if the valve will not stay open. When that happens, the hydraulic oil is probably leaking past the piston or through the packing gland.
If the valve will not close when hydraulic pressure is released, check for a broken spring or binding of the stem. The stem may bind because the packing is too tight.
Before you repair or replace parts in a magazine sprinkling system control valve, close the firemain cutout valve in the supply line to the control valve, then drain the supply piping.
DUAL SOLENOID CONTROL VALVES
The dual solenoid control magazine sprinkling hydraulic-operated valve. good knowledge of electricity or have an elec-When you work on this valve, always have an electrician working with you. There are two good reasons for this: (1) a beginner could accidentally flood a compartment; and (2) unless you have a valve is an electric-trician, you are taking a risk.
Table 5-3.-Troubleshooting Chart for Main Valve of the Dual Solenoid Control Valve
Table 5-3.-Troubleshooting Chart for Main Valve of the Dual Solenoid Control Valve-Continued
The dual solenoid control contains two 440-volt solenoids and one microswitch with an actuator operated by mechanical linkage. Even after the mechanism has been de-energized, there is some danger of electric shock. Do not work on this valve until an Electrician's Mate has disconnected, removed, and insulated (taped) the electrical leads from the valve. You should avoid contact with the insulated leads even though you are certain they are de-energized and properly insulated.
The operating principle of the dual solenoid control valve goes back to the pressure spring and diaphragm theory. However, the actuating device is different. It is an electric switch that controls a plate-type valve. When the switch is closed, firemain pressure is constantly on top of the diaphragm. The firemain pressure, plus the spring pressure, keeps the valve closed. When the switch is opened, the plate valve rotates, closing off firemain pressure to the top of the diaphragm, and allowing what pressure is there to drain off. Now the firemain pressure beneath the diaphragm is greater than the spring pressure above, and pushes the diaphragm up to open the valve.
As long as the solenoid control valve does not leak and turns freely when manually operated, no preventive maintenance is required. Normal operation, followed by thorough flushing, should be enough to keep the valve in good working condition. If fog-foam solutions are used, you should flush and operate the valve several times to remove foam from the solenoid pilot valve system. This valve has few operational difficulties. The troubleshooting suggestions in table 5-3 should cover all corrective maintenance that may be necessary.
In addition to the troubles described in table 5-3, you may at times have trouble with leakage from the solenoid pilot valve connection. If this leakage is confined to a slow drip, the valve operation will probably be normal and it will be possible to dispose of the drain water easily. No corrective action is required in such a case, but you should look at the valve periodically to see if the leakage is increasing.
If there is too much leakage, it will be necessary to repair or replace the pilot valve.
Remove the tubing from the drain connection and put the leaking pilot valve in the closed position. You will see that the leakage comes across the lapped surfaces of the disk and distributor. These are the parts upon which you will have to make the repairs.
As you disassemble the valve, carefully note the position of both the disk and the distributor in relation to the mounting holes. Lap the disk and the distributor to a mirror finish, and as flat as possible. Use a figure-eight motion on a fine, flat Carborundum stone, and avoid crowning the disk while lapping. You can use a lapping block with a medium grit compound. But you must wash the parts in a clean solvent to remove every trace of abrasive, and then bring the surfaces to a high polish.
Coat the lapped surfaces with a thin coating of any high-grade waterproof grease, and then squeeze the surfaces together. Replace the parts exactly as they were before disassembly.
To test the pilot valve, apply pressure at the supply point and rotate the stem several times. There should be no leakage when the valve is in the OFF position.
This chapter covered various kinds of firefighting equipment and systems. All systems are not alike from one ship to the next. You will need to trace out the systems on your ship. Use the manufacturer's technical manuals to help you study your systems. To be efficient in fire fighting, you should know how to operate all of the fire-extinguishing systems and which areas of the ship these systems protect.
This chapter also covered compressed-gas cylinders and the safety precautions involved in working with them and the maintenance and repair of valves used in fire-fighting equipment and systems.