How should knife gate valves be maintained?

Knife gate valves are used to shut off a variety of solid-containing media applications, including oil sand slurries, pulp feedstocks, mines, wastewater treatment, power stations, and more. Routine maintenance and repairs are also very important to ensure normal use.

1. Adjust the filling once a month.

2. Lubricate the valve stem and valve stem nut every three months. This should be done using a grease gun at the grease filler port on top of the bracket.

3. Lubricate the gear operating mechanism once a year.

Filler

When the knife gate valve is not used for a long time, the valve should be cycled at least every six months. If stored, the packing should be loosened to extend the service life of the packing.

It is also important to tighten the packing gland as needed. When adjusting the packing on a valve with four or more bolts, it is best to use the cross-torque method to evenly tighten the bolts on both sides of the packing gland. Usually only a small amount of tightening is required. Do not overtighten to stop leaks; adjust the packing gland downward as evenly as possible to avoid the possibility of the gland rubbing against the gate as the gate moves.

With regular inspection and lubrication, depending on the cycle count and chemicals used, the operator will know when the packing or seat needs to be replaced. If maintenance is required, safety first:

1. Close all operating lines of the valve.
2. Completely isolate the valve from the process.
3. Release process pressure.
4. Drain the process fluid from the valve.

Replace packing

Standard packing kits are available from knife gate manufacturers and their distributors. Packing kit includes necessary packing to ensure a tight seal. When ordering a packing kit, be sure to specify the valve model number, seat type and valve type.

Safety first: Relieve valve pressure and make sure it is closed.

1. Remove the packing gland nuts and bolts.
2. Lift the gate to the fully open position.
3. Pull the packing gland up to the top of the gate and secure it to the top of the gate.
4. Use a packing hook or screwdriver to remove all old packing.
5. Clean the packaging box carefully.
6. Using the pre-cut packaging kit, insert the packages one row at a time into the box. Use a flat steel tool to tap each row of filler into place. Packing joints should be 180° apart.
7. Pull down the packing gland and tighten the nuts and bolts using the cross torque method. Do not overtighten.
8. Bring the valve to operating pressure and tighten the packing gland sufficiently to stop any leakage or dripping. Over-tightening of the gland will result in shortened packing life.

Valve seat replacement

To replace the valve seat, first remove the valve from the line.

Two-way perimeter seat

1. Disconnect the valve stem U-shaped clamp from the gate, and remove the valve yoke and valve stem assembly. Remove the packing gland, packing and valves.
2. When removing the valve seat, you may need to use a pair of vise grips to securely hold the valve seat and wire insert, and possibly use a spring to pull the old valve seat out of the valve body. At the bottom of the valve, the seat groove has a retainer flange, and the rubber seat must be pulled through this narrow opening.
3. To install a new valve seat and repackage the valve, reverse the steps. First, place the new valve seat into the valve body seat cavity by bending the valve seat into a horseshoe shape, and then insert it into the valve seat cavity. Take a three- or four-foot piece of flat steel about 3/8″ x 2″ or 3″ wide and hammer the seat into the bottom of the valve and along the sides as firmly as possible.
4. Insert the valve when the valve seat is in place and the ends of each side protrude above the stuffing box. Install the yoke and stem assembly and move the gate to the bottom position, making sure the valve seat is pushed into its retainer groove along the bottom and sides.
5. When the valve seat is fully seated, remove the valve yoke and valve stem assembly. Repack the valve and place the packing strips on each side of the gate so that they run the full length of the stuffing box. Make sure the stuffing is cut long enough and fits snugly at both ends of the stuffing box. When the valve gland is filled, use a hacksaw to cut off the excess rubber seats above the stuffing box on each side.
6. Install the packing gland and reinstall the valve yoke and stem assembly.
7. Stroke the valve for a complete cycle to ensure easy operation and that the valve body or packing gland will not rub against the gate.
8. Under pressure, tighten the packing gland bolts only enough to prevent packing leakage.

Troubleshooting table

While the maintenance schedule and procedures for knife gate valves are fairly simple, there are some details and operational issues that can add or change maintenance requirements. By understanding these variables and adjusting maintenance accordingly, you can extend the life of your valve and reduce your total cost of ownership.

Resilient Seated Knife Gate Valves

1. Problem:

   Leakage from packing

   Solution:

   Tighten the packing gland bolts/nuts evenly and slowly. Usuallyonly a 1/8 to 1/4 turn on the bolts/nuts will stop the leakage.Onlytighten bolts/nuts enough to stop the leak.

2. Problem:

   Seat leakage

   Solution:

   The gate may not be completely closed due to an obstructionbetween the gate and the seat. Open the gate to 1/4 open andthen close to fully closed position.Check for seat leakage.

3. Problem:

   Valve difficult to operate

   Solution:

   1. Lubricate stem and stem nut.Check for improvement.
   2. Loosen packing gland bolts a small amount (not enough to causea leak around the gate packing). Check for improvement.
   3. If problem persists consult the factory.