THE ORIFICE SLIDE GATE VALVE: WHAT MAKES IT DIFFERENT FROM OTHER FLOW CONTROL VALVES SUCH AS BUTTERFLY VALVES AND BULL NOSE KNIFE GATES?
The fundamental difference is the Quantum Series Orifice Slide Gate is designed specifically to handle dry material like powders, pellets and granules. Valves such as the butterfly valve and the bull nose knife gate are designed to be used in gas and liquid applications and suffer numerous problems when misused in a dry bulk handling application.
The butterfly valve’s design creates a handling problem for dry bulk solids, as the disc is located in the immediate flow stream of material. This creates a significant flow restriction and many engineers design the entire conveying system with larger piping than necessary to accommodate this bottleneck in the valve.
The soft seals can promote another problem. A butterfly valve relies on the soft seals that allow the disc or blade to produce a bubble-tight seal in the closed position. These seals erode and tear over time. The very nature of dry solids does not allow these types of valves to create a tight seal because dry material cannot be displaced like a gas or liquid.
The exposed soft seat of the butterfly valve is also susceptible to blast abrasion by material flow. This causes additional wear points and eventual leakage of material and/or conveying pressure through the valve, even when the valve is in the closed position. In a powder handling application, particles tend to migrate through the stem of the butterfly valve causing the valve to seize.
Soft-seated knife gates would seem more logical for dry solids handling than butterfly valves. However, the soft seals typically used for gases and liquids are also exposed to blast abrasion from dry bulk materials. Upon closing, the leading edge of the blade tends to compact material into the soft seals, causing seal abrasion and can prevent the gate from completely closing. The packing gland (the sealing area designed to prevent air and material from escaping into the bonnet) of the valve is also exposed to abrasion as material migrates through the packing seals on opening and closing strokes. Once the packing gland seals are worn, conveying air and material are allowed to escape into the atmosphere.
With both designs, replacement or rebuilding of the valves can be cumbersome and create extensive downtime as butterfly valves and knife gates are made from heavy metal cast. This adds a significant amount of unnecessary weight to the valve which can make it difficult to install. If maintenance is required, both valves lack in-line maintenance features so they will have to be removed from the conveying line to be worked on. This can require extensive downtime and it some cases, it is cheaper to replace the entire valve rather than replacing new seals and parts.
The problems that occur with butterfly valves and knife gates are eliminated with the Orifice Gate design. It utilizes a stainless steel, rectangular plate with a circle machined through it. The machined plate then actuates between two compression-loaded hard polymer seal plates. In the closed position, the compression load on the blade prevents material and conveying air from escaping through the valve or into the plant’s atmosphere. In the open position, the orifice in the blade aligns with the conveying line, thus eliminating flow obstructions or exposed seals that might be vulnerable to blast abrasion. The valve also “self-cleans” material from the seat on each stroke of the blade so there is no bridging or packing of material.
The Quantum Series Orifice Gate’s hard polymer seals compensate for wear unlike the butterfly valve and the knife gate. The seals are also adjustable without removing the valve from service reducing downtime costs. If the valve ever does need to be removed from the conveying line, its modular construction is lightweight compared to cast valves.