Key points for inspecting the manhole cover and pressure relief valve of the export tank semi-trailer

The manhole cover and pressure relief valve of the export tank semi-trailer are the core safety components of the tank body. Overseas travel is bumpy, with large temperature differences and various types of media. Many leakage and deformation problems of the tank body come from the workmanship defects of these two accessories. When purchasing and factory acceptance, it is not enough to only look at the appearance, but to verify each detail item by item. Priority should be given to the substrate for manhole covers. The mainstream choice is die-casting aluminum alloy, with a uniform thickness of the plate surface and no sand holes, air holes, or shrinkage holes. Poor quality castings have loose interiors and are prone to cracking under long-term pressure. The flange sealing surface should be flat, without burrs or deformation, and the sealing groove depth should be consistent to avoid leakage due to uneven stress on the gasket. The locking and clamping mechanism is the key point. The cam and clamping handle rotate smoothly without jamming, and the pin position is quenched to prevent rapid wear after repeated opening and closing. The style with a secondary pressure relief structure is preferred. Before opening the lid, the residual pressure in the tank should be released to avoid safety risks during overseas operations. The sealing ring material should match the transportation medium. Nitrile rubber can be selected for ordinary oil, and fluororubber must be used for corrosive chemical media. The rubber material is dense, without bubbles or missing materials. The anti rollover sealing structure should also be checked to prevent medium leakage in case of accidental rollover of the vehicle. The pressure relief valve, also known as the pressure vacuum breathing valve, first checks the nameplate information to ensure that the set pressure, vacuum value, and medium compatibility are clearly and permanently labeled, in compliance with the target market regulations. The valve body is also checked for casting quality, and the valve disc and guide rod move flexibly without jamming. The spring elasticity is stable, and poor quality springs are prone to fatigue, resulting in normal opening or failure to open in high temperature and low pressure environments. The sealing surface needs to be finely ground and tightly adhered after closure. It must undergo an air tightness test before leaving the factory. When the pressure reaches the set value, it should be stably opened and reliably reseated after the pressure drops, without continuous air leakage. The filter screen cannot be ignored. The filter screen has a uniform aperture and is firmly fixed to prevent impurities from blocking the valve plate. Many remote overseas construction sites do not have maintenance conditions, and damage to the filter screen can easily lead to the failure of the pressure relief valve. It is also necessary to check the matching welding base and anti-corrosion treatment. The flatness of the flange connecting the manhole seat and the tank body should meet the standard, and the welding should be full and free of slag and air holes. The surface of the valve body should be anodized or sprayed with anti-corrosion coating to adapt to sea transportation and long-term operation in rainy and saline alkali areas. Before delivering to overseas customers, in addition to static visual inspection, try to conduct inflation and pressure tests as much as possible, and prepare vulnerable spare parts such as sealing gaskets and springs of the same specifications. Notify the fleet in advance to regularly clean the sediment inside the valve to avoid medium crystallization and sediment accumulation affecting the pressure relief function. Use effective work and supporting solutions to reduce the safety hazards of cross-border transportation leakage and minimize customer downtime losses.