Maintenance of globe valves

For a functioning globe valve, all components must be present and in good condition. The bolts on flanges and supports are essential; the threads must be intact with no signs of looseness. If the nuts on the handwheel become loose, they should be tightened promptly to prevent damage to the connections or loss of the handwheel and its markings. If the handwheel is lost, it must not be replaced with a adjustable wrench; a new handwheel must be obtained immediately. The packing gland must not be misaligned or lack any pre-tightening clearance. For globe valves located in environments prone to contamination by rain, snow, dust, or sand, a protective cover must be installed on the valve stem. The markings on the globe valve must remain complete, accurate, and clear. The lead seals, caps, and pneumatic accessories must also be intact. It is strictly prohibited to strike, stand on, or place heavy objects on a functioning globe valve. This is especially true for non-metallic and cast-iron valves. Maintenance work on valves before welding, before commissioning, and after commissioning is crucial for ensuring their proper function and extending their service life. Proper and orderly maintenance will protect the valves and enable them to perform their duties effectively. Although valve maintenance may seem simple, there are often overlooked aspects. 

First, when lubricating a globe valve, the amount of grease used is often neglected. After selecting the appropriate valve and lubrication method, the operator proceeds with the lubrication process. There are two potential issues: too little grease can lead to accelerated wear of the sealing surface due to lack of lubrication, while too much grease results in waste. The correct amount of grease should be determined based on the valve type and its sealing capacity. The sealing capacity can be calculated using the valve’s dimensions and category, and an appropriate amount of grease should then be applied.

Second, the pressure during grease injection is also often overlooked. During lubrication, the pressure fluctuates regularly. Too low pressure can cause sealing leaks or failure, while too high pressure can block the grease inlet, harden the grease inside the seal, or cause the seal to stick to the valve ball or disc. When the pressure is too low, the grease tends to flow to the bottom of the valve chamber, especially in small gate valves. High pressure, on the other hand, can cause problems such as clogged grease nozzles or hardened grease. In such cases, a cleaning solution should be used to soften the hardened grease, and new grease should be applied. The type and material of the seal also affect the required lubrication pressure. Different seal types require different pressures; generally, hard-sealed valves require higher pressure than soft-sealed valves. Ball valves are usually maintained in the open position unless special circumstances require them to be closed. Other valves cannot always be assumed to be in the open position. Gate valves must be closed during maintenance to ensure that the grease fills the sealing grooves along the seal. If they are open, the grease will flow into the flow channel or valve chamber, resulting in waste.