Flowserve Double-Disc Gate Valve Sizes 2.5 - Manual (Page 22)

Anchor/Darling Double Disc Type Gate Valves FCD ADENIM0003-01 - 07/14
22
withdrawn squarely from the body neck bore. The slightest
cocking of the bonnet during withdrawal can cause it to bind
and can damage the pressure seal area of the body.
Therefore, it is recommended prior to removal, that the square-
ness of bonnet and gasket with respect to the body be checked.
This is most easily accomplished by measuring the distance
between the top of the gasket and top of the body neck. If the
gasket is not square, it should be tapped with a brass rod until it
is.
With large bonnets it is a good idea to periodically check the
squareness of the bonnet as it is being withdrawn.
Binding any time during withdrawal indicates the bonnet has
cocked. Further efforts to force the bonnet will generally make
the situation worse. At the first sign of binding, stop and check
the squareness of the bonnet.
6.3.7 The preferred method of lifting the bonnet (Fig. 17) is by using
slings attached to the gland retainer (131).
This means of lifting minimizes cocking. In order to attain the
best attachment, the gland bolts (209) should be removed and
the retaining rings’ halves reassembled on the bonnet.
If desired, the sling can be looped through the retaining ring
ears prior to assembly on the bonnet.
Attempting to remove the bonnet by raising the stem, either
with slings or the actuator, is not recommended. The load
between the stem and the bonnet will be imparted to the
backseat.
Excessive force on the backseat-sealing surface may cause it to
deform or crack.
6.3.8 Following the above procedure will, in most cases, result in
removal of the bonnet with little difficulty. However, certain
circumstances, such as installation of the valve with stem in
other than a vertical orientation, may cause complications.
If greater difficulty is encountered, a Flowserve service engineer
should be consulted. Excessive force, which may damage
critical surfaces, should be avoided.
Figure 17