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Valves used in recycling, cleaning and de-trashing processes have to stand up to a lot. Metal rejects, wire, glass, sand and other debris can cause physical damage to valve gate and seats, causing clogging in valve bodies, leakage in valve packing, and leaks due to abrasion and wear.
If you’re in need of a more robust recycle/reject trash valve, we recommend specifying these 7 features to ensure your valve has a fighting chance against such a challenging environment.
Upgrading to a 17-4 PH stainless steel gate will offer additional strength and longevity.
Further upgrade to a 400 series stainless gate for additional abrasion resistance. This is commonly found in cyclone cleaner applications.
And finally, hardening the gate with a stellite coating (cobalt and chromium alloy) will give the gate an even harder face. This may allow it to shear through troublesome debris, like staple chains, that may get hung up in the seat channel and otherwise prevent the gate from fully closing.
As with the gate, the seat should also be hardened with stellite or an overlay to hold up to debris and abrasive media found in cleaning applications.
The option of a replaceable metal seat may be necessary in extremely abrasive applications. This option allows the seat of the valve body to be easily replaced and can significantly increase the valve service life.
The wedges should also be hardened to help maintain as tight of shut-off as possible.
An oversized cylinder will deliver more force for the gate to potentially shear through debris and obtain a tight close.
This cylinder may be two to three sizes larger than required for normal knife gate valve applications.
With the oversized cylinder a self-supporting yoke is necessary to support the increased size and vibration commonly found in these applications
Replace the bottom row of packing with Kevlar. The Kevlar acts as a scraper to help clean the gate and protect the additional rows of packing.
Live load the packing with Belleville disc spring washers to ensure continuous pressure.
The packing gland should be stainless steel to handle the wet environment.
Unlike a normal metal seated knife gate valve that uses line pressure to assist with seating, the valve should be installed in a reverse orientation. This helps eliminate the buildup of debris and media in the seating area of the valve, which could prevent the gate from fully closing.
Utilization of backing rings or chest buttons (set-screws) to support the gate may be necessary due to the reversed valve installation.
Flush ports are threaded NPT taps in the body and chest of the valve. This allows for flush water to be piped into the valve to help clear debris that may be hung up in the seating area and chest cavity.
Make the proper selections next time you need to replace a recycle/reject trash valve. Implementing these 7 features will help ensure the longest life possible for the valve. Talk to an engineer that specializes in valves and paper processes to select the best valve for your application.
Got a question about sizing and selection of valves? Ask us about it! We gladly provide technical advice to businesses and municipalities in Wisconsin, Minnesota, Iowa, and upper Michigan.