Low-temperature valve failure troubleshooting

Common Issues with Low-Temperature Valves: Gearwheel stuffing box leakage; valve cover nut leakage; internal leakage in the valve; leakage at the valve-pipe connection.

Leakage at the handwheel stuffing box or valve cover nut can be tightened with a wrench when the storage tank is not pressurized; it is strictly prohibited to tighten under pressure.

Valve internal leakage is usually caused by solid particles in the valve stem or wear from frequent opening and closing. Both the inlet and outlet valves are double-valve designs, with one in reserve. When internal leakage is detected, close the reserve valve and repair the leaking valve. First, loosen the valve cover nut with a wrench, remove the valve rod, and dry the valve disk and cover rod with a hair dryer; then clean the valve body sealing surface and the valve disk sealing gasket, and wipe away any condensation or water. If the valve disk gasket has unevenness, cracks, or grooves, replace it immediately with a spare gasket. If the valve body sealing surface shows wear marks, smooth it with metallographic sandpaper (if unavailable, use the back of fine wood sandpaper). Before reassembly, carefully remove any dust, condensation, or water, and tighten the valve cover nut.

When leakage is found at the valve-pipe connection, please have a qualified unit perform the repair. During the repair, drain the liquid completely and vent it. For oxygen equipment, the oxygen content must be reduced to less than 21%. Before welding, position the valve halfway open and loosen the valve cover nuts. After welding, retighten the nuts and conduct an air tightness test on the pipeline.

Pressure (Level) Gauge Fault Handling

Common issues include malfunctioning indicators and pointer trembling.

1) A malfunction in the indicator can be categorized as either the pointer failing to return to zero or the pointer remaining fixed at a certain value. If it's the former, it's usually due to improper use, such as the combined valve of the differential pressure (level) gauge not being in a balanced state before filling, causing the pointer to not return to zero. Open the combined valve after liquid enters through the lower inlet. If the deviation between the pointer and zero is minimal, you can loosen the screw holding the fixed gauge needle, adjust the pointer to zero, and then tighten the screw again.

2) Pointer jitter is usually caused by air leakage in the gauge tube. Carefully inspect the gauge tube, combination valve of the level gauge, and related connections of the pressure gauge. Additionally, if overfilling with liquid causes a differential pressure (level) gauge to intake liquid, the tube may also exhibit jittering.

(4) Summary of Fault Handling Methods

Potential faults during use, their causes, and solutions are listed in the following table.

Troubleshooting Methods

Fault Phenomenon    Reason    Solution

During use, internal pressure

Abnormal Increase Occurred a. Turbine inlet valve not sealing properly, resulting in internal leakage. Turbine inlet valve to be ground and inspected.

b. The pressure gauge reading is inaccurate. Inspect or replace the pressure gauge.

Pressure (Level) Gauge Indication is Inaccurate a. Pressure (Level) Gauge Malfunction. Inspect the Pressure (Level) Gauge.

b. Leakages in the upper and lower pipes of the differential pressure (level) gauge. Repair and seal.

c. Leaking at the differential pressure (level) gauge connection. Repair and remove the leak.

Evaporation rate exceeds design

Value, Sweating and Frost on Top a. Air phase vent valve not tightly closed, internal leakage. Valve grinding and inspection required.

b. Degradation in vacuum level. Re-evacuate the vacuum.

c. Top pearlescent sand has settled, sand is not fully packed. Refill pearlescent sand, re-purge vacuum.

Leakage of liquid or gas from the valve cap or joint: a. The sealing packing is not tightly pressed. Tighten the gland nut.

b. Sealed ring damaged. Replace the sealed ring.

c. Seal face damage. Repair or replace parts.

d. Weld Seam Leaks - Repaired Welding (but should be carried out according to repair welding specifications).