Repairing Sealing Surfaces of Marine Globe Valves

Repairing Sealing Surfaces of Marine Globe Valves


Combined with the work practice on board, aiming at the damage to the sealing surface of the boiler feedwater globe check valve, the method of grinding the sealing surface to repair the glove valve is introduced for the reference of the general engineers. The valve is a pipeline accessory used to control the flow, flow direction of the medium as well as opening and closing of the pipeline. A globe valve is one of the most common valve parts, and it is also the most widely used marine valve. It is mainly used in seawater, fresh water, fuel oil, lubricating oil and steam pipelines with a temperature below 225°C.
 
Causes and hazards of damage to sealing surfaces 
Coupled with the frequent opening and closing, pitting and dents often appear on the contact surface between the valve disc and the valve seat of the globe valve due to the corrosive effect of the medium or the impurities contained in the medium, and even grooves are formed in severe cases, causing the globe valve to fail. Leakages due to not being closed well will bring inconvenience to the daily operation of the pipeline system, and even cause failure of the main and auxiliary machinery in the engine room.
 
The countermeasures of the damaged sealing surface
For the globe valve not being closed well, the usual solution is to grind the sealing surface or replace the valve with a new one. Most of the ships are equipped with various types of valves for replacement, and because of the high price of large-sized valves, most people choose to grind the sealing surface during ship repair. If the sealing surface of the glove valve is damaged and there is no suitable valve on board to replace it, it must be ground by the ship's personnel. There are no special grinding tools on most ships, and if you are not experienced enough, it is easy to mistakenly grind the sealing surface, resulting in unsatisfactory results.
 
For example, a ship has 2 groups of boiler water supply systems, one for use and one for standby. Each group is controlled by 4 valves, of which 2 globe check valves are installed on the boiler body; the inlet of the feed water pump is a globe valve, and the outlet is a globe check valve (Figure 1). One day, the boiler feed water pump did not pump water; the boiler water level was low and the alarm was given, and then the boiler was shut down; the other pump was not supplied with water, and it was found that the two pumps were full of steam when the air was released from the two pump bodies. After inspection, it was found that the three globe check valves of the outlet pipeline of the No. 1 feed water pump were not closed well, and the globe check valve of the outlet of the No. 2 feed water pump was also not closed well. The steam flowed backward from the boiler to the feed water pump and the inlet pipeline of the pump, resulting in 2 pumps not pumping water. Fortunately, it is during the resting period, the furnace can be shut down for maintenance. If this happens during operation, the shutdown of the furnace will affect the operation of the main engine, and the consequences will be disastrous. The two sets of water supply system valve parts were disassembled and inspected, and it was found that there were pits and grooves on the sealing surface, and manufacturing quality of some valve parts was poor and the sealing surface was rough and uneven. The ship is newly received, and there are few valve parts in stock; there is no valve of this type at all. The above problems must be solved by grinding the sealing surface.
 
The diagram of the boiler water supply system
Figure 1 The diagram of the boiler water supply system 

The usual way to grind the globe valve is to put the valve disc on the valve seat for grinding, but the contact surface between the valve disc and the valve seat is very small, and it is difficult to align. Therefore, the contact surface is easily ground to the wrong side, and the grinding effect is not good. You need to change your mind, and find another way. The method of grinding the sealing surface of the exhaust valve of the main engine can be used for reference, that is, the air valve and the valve seat are ground separately using a special grinding tool, and the valve disc and the valve seat of the globe valve are ground separately. There are grinding plates on board, and the plane of the valve disc can be ground on the plate. The grinding method of the valve seat is shown in Figure 2, which is as follows:
(1) Find a round steel rod; turn the lower end surface flat and turn the outer circle diameter slightly smaller than the valve body hole; use the valve body hole as the guide to seal the valve seat 
(2) You can also turn the outer diameter of the lower end of the steel rod to be slightly smaller than the hole diameter of the valve seat, and use the seat hole as a guide to grind the sealing surface of the valve seat. It should be noted that the grinding surface of the steel rod should be smooth and flat.
 
The schematic diagram of grinding the sealing surface of the globe valve
Figure 2 The schematic diagram of grinding the sealing surface of the globe valve

Using these two methods, the sealing surfaces of the four globe valves and globe check valves were ground, and the effect was very good. There was no backflow of boiler water after reinstallation.
 
Grinding methods and promotion of sealing surfaces of large globe valves
For some larger globe valves, this method can also be used to grind the sealing surface. Use some common parts, such as screws, nuts and flanges to make simple grinding tools, as shown in Figure 3. The disc 1 acts as a guide, and the disc 2 is used to grind the plane of the valve seat. The disc can be used for processing flanges. The key to making the grinding tool is that the center line of the circular plate and the screw rod should coincide, and the outer circle of the circular plate 1 should closely match the hole of the valve body; the hardness of the circular plate 2 should be great, and the lower plane should be smooth and flat.
 
Plan view of the grinding tool
Figure 3 Plan view of the grinding tool

Globe valves are standard parts. For the same type of valve parts, the size of the valve seat hole or valve body hole should be the same. According to the above method, discs of different sizes can be processed, special tools for grinding valves can be made, and different types of globe valves can be ground.
 
Conclusion
There are hundreds of globe valves in a ship, and they are often not closed well. Most of the problems can be solved by grinding the sealing surface without replacing them, thus saving a lot of money.