Paper360 - November/December 2015 - (Page 22)
maintaining knife Gate Valves
Even the simplest valve designs need regular maintenance.
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.
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
* 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
Figure 4. Tap down each row of packing into
place using a flat bar tool. Source: Lined Valve
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
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
* Release process pressure.
* Drain the process fluid from the valve.
Table of Contents for the Digital Edition of Paper360 - November/December 2015
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
Index of Advertisers
Paper360 - November/December 2015