Paper360 - November/December 2015 - (Page 22)

millwise | MAINTENANCE maintaining knife Gate Valves Even the simplest valve designs need regular maintenance. VIKKI PYNENBURG 22 Knife gate valves are one of the simplest valve designs, but still require maintenance. With only one moving part, the preventive maintenance schedule is not brutal, but certainly should be habit forming. It includes adjusting the packing once a month, lubricating the stem and stem nut every three months, and lubricating the gear operator once a year: * Lubricate the valve stem, using a grease gun at the grease fitting at the top of the yoke. * Tighten the packing gland as needed. When adjusting packing on valves with four or more bolts, it is best to tighten the bolts evenly on both sides of the packing gland using the cross torque method. Normally, just a small amount of tightening of the bolt is required. Do not over tighten to stop a leak. Try to adjust the packing gland down evenly to avoid the possibility of the gland rubbing on the gate as it moves. * Seat (resilient seated only) maintenance. When knife gate valves are not in use over a long period of time, the valve should be cycled at least every six months, and if in storage, the packing should be loosened to extend its life. With this regular inspection and lubrication, which depends on the cycle count and the chemicals at play, the operator will see when packing or seats need replacing. This article will outline how this takes place at the mill. REPLACEMENT PACKING Standard repacking kits are available from knife gate manufacturers and their distributors and contain necessary packing to ensure a tight seal. When ordering packing kits, be sure to specify the valve model number, seat type and type of valve. Safety first - release pressure from valve, making sure the valve is closed: * Remove packing gland nuts and bolts. * Raise gate to full open position. * Pull up the packing gland to the top of the gate and secure it to the top of the gate. * Using a packing hook or screwdriver, remove all the old packing. * Carefully clean the packing box. * Using a pre-cut packing kit, insert packing one row at a time into packing box. Tap down each row of packing into place using a flat bar tool. Packing joints should be located 180° apart. * Pull packing gland down and tighten nuts and bolts using cross torque method. DO NOT OVERTIGHTEN. * Bring valve up to working pressure and tighten the packing gland just enough to stop any leaks or drips. Over tightening of the gland will result in reduced packing life. Figure 1. In preparation, all tools and packing kit ready, old packing removed. Source: Lined Valve Company, 2015. Figure 2. Packing gland nuts and bolts are removed, gate raised to full open position Source: Lined Valve Company, 2015. Figure 3. Insert packing one row at a time into packing box. Source: Lined Valve Company, 2015. Figure 4. Tap down each row of packing into place using a flat bar tool. Source: Lined Valve Company, 2015. Figure 5.Packing joints should be located 180˚ apart. Source: Lined Valve Company, 2015. Figure 6.Replacement packing complete, pull packing gland down, tighten nuts and bolts using cross torque method. Source: Lined Valve Company, 2015. Paper360º SAFETY FIRST Before performing any maintenance on a knife gate valve, safety comes first: * Shut off all operating lines to the valve. * Isolate the valve completely from the process. * Release process pressure. * Drain the process fluid from the valve. NOVEMBER/DECEMBER 2015 www.tappi.org http://www.tappi.org

Table of Contents for the Digital Edition of Paper360 - November/December 2015

Setpoint
Over the Wire
Proud to be a Papermaker
Solenis’ Total Mill Perspective Helps Mills Stay Competitive
Maintaining Knife Gate Valves
An Automated Solution to the Kappa Number Test by Titration
Higher Alloyed Composite Tubes Make Recovery Boilers Safer and More Efficient
TAPPI Journal Summaries
New Leadership Model Focuses on Caring, Compassion
Consolidation Watch
Association News
ASPI News
Online Exclusives
Index of Advertisers

Paper360 - November/December 2015

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