Cast steel check valves have some easily overlooked but crucial “hidden knowledge” that directly affects their effectiveness and lifespan!
1. The gateway in the material
Cast steel “does not mean casual use: valves marked with WCB material may seem universal, but in actual casting, if trace amounts of molybdenum elements are added (such as welding 507 molybdenum), the corrosion resistance will be significantly improved, making them suitable for chloride ion or acidic medium environments.
Cutting corners on springs: Some low-priced valves use ordinary carbon steel springs, which corrode and cause a decrease in elasticity, resulting in slow valve disc closure, easy backflow, and even pipe bursting.
2. Design flaws
The shape of the valve disc hides mysteries: the lifting valve disc (cylindrical) has high resistance but good sealing performance, suitable for small-diameter pipelines, but it is easy to get stuck when used with large diameters; The rotary valve disc (disc-shaped) has low resistance but poor sealing. When installed vertically, if the medium flow rate is low, it may not close tightly.
Be cautious with clamp type valves: Although they are cheap and lightweight, the valve body is prone to deformation under high pressure, and uneven stress on flange bolts may cause leakage.
3. Hidden risks of installation and use
The illusion of ‘can be used even if installed upside down’ is false: installing the valve body in the direction of the arrow upside down may not cause an error in the initial stage, but over time it can lead to abnormal wear of the valve disc, increasing the probability of sudden bursting.
Vertical pipeline trap: When installing a swing check valve in a vertical pipeline, it is necessary to ensure that the medium flows from bottom to top, otherwise the valve disc cannot be reset under the action of gravity.
The ‘gentle trap’ at the outlet of the water pump: When the water pump suddenly stops, high-speed reverse flow may impact the valve disc, causing a ‘water hammer effect’, and the brittle cast steel valve body may crack directly.
4. Maintain cold knowledge
Scaling on the inner wall can lead to “chronic murder”: impurities in the medium accumulate around the valve seat, which may not seem to affect use, but in reality can cause the valve disc to not close tightly, resulting in high-frequency vibration during backflow and ultimately tearing the weld seam.
The saying ‘if it’s not broken, there’s no need to repair it’ can be fatal: if the valve doesn’t operate for a long time (such as at the outlet of a backup water pump), the valve disc may stick to the valve seat and become stuck and ineffective during emergency start-up.
5. Disguising characteristics of inferior products
The weight is not right: valves that cut corners will use thin-walled castings, which are 10% -15% lighter than genuine products of the same model.
Exposure problem of knocking sound: When lightly tapping the valve body with a hammer, the sound may be dull with sand holes, but if it is crisp, the internal structure will be uniform.
Valve disc “virtual fat”: Poor quality valve discs have rough surfaces and deliberately thicken to cover up defects, resulting in lower actual strength.
Mastering these ‘industry jargon’ can avoid 80% of pitfalls when selecting and installing valves.