The how (and why) of maintenance part 8
The lubrication fittings
To be able to perform maintenance on valves; inject valve cleaner, lubrication or sealing component there is a need for injection points that connects the lubrication canals in the body and to the seat; as illustrated in figure 42. On a trunnion ball valve there should be an inner check valve installed on the inside of the lubrication fitting, as illustrated in figure 42 and 43, the pressure from the inlet pipe goes directly up the lubrication canal and stops at the check valve in figure 43 but in figure 44 the pressure from the pipe goes directly towards the lubrication fitting as a single point of barrier.
Figure 42 Figure 43 Figure 44
There are a large variety of lubrication fittings or grease fittings as most call them, and unfortunately some of them should not be used in high pressure or hydrocarbon systems. The fittings illustrated in figure 42 – 44 are one of those absolutely not recommended. Most of you will probably see why: There is no cap on the outside of the fitting. If there should be corrosion or damage to the check valve and the internals of the fitting, or some mechanical damage by equipment bumping into the fitting on the outside, you could be in deeep shit. The illustration in figure 44 is one absolutely prohibited! But I have seen it on old plants (witch is even worse).
Figure 45 Figure 46
Looking at figure 45 you can se the fitting consist of a body, a check valve and a cap with went holes. Before doing maintenance on the valve the cap is loosened and the check valve is tested before the cap is taken off. If there should occur a leak one can tighten the cap and no damage done.
Before we go on further we should look at the difference in the setup of lubrication fittings in the parallel gate valve and the ball valve. Looking at figure 46, illustrating a solid slab parallel gate valve one can se that the lubrication fitting are connected to the cavity of the valve, and if there are fittings installed to the seats of a parallel gate valve the canals from the fittings will always enter on the cavity side of the seal area of the seat. The reason for this being; it is always the downstream side of a parallel gate which is the main seal. Compared to the trunnion ball valve, which seals from the upstream side. Having a parallel gate valve with spring energized seats that seals on both up and downstream side (radial seals on the seats) will pose as a barrier towards the lubrication fitting, and in the most cases there will be no inner check on the inside of the fitting. But if the valve is equipped with seats that only seals on the downstream side the pressure from the inlet side of the valve will not be stopped by the upstream seat and consequently there should be a inner check on the inside of the fitting. As fare as my experience goes, there are a mixture of everything, made by personnel by changing equipment without knowing the basic.
Going back to the trunnion ball valves and looking at figure 47 it is clearly without an inner check. The fitting illustrated in figure 47 is two pies, so called double block fitting, normally consisting of two inner checks and a mechanically locked seat. To be able to inject anything into this fitting one must unscrew the blue part ½” – 1 turn (lifting the seat) before injecting anything. But even thou there are two check balls and a mechanically locked seat, I am not too happy about being without an inner check. There are two reasons: What happens if the relatively long fitting is accidental being hit by a heavy object and broken of. And the other reasons: As I previously on several occasions have stated: I don´t like NPT. In fact, my personal opinion is that NPT should be banned on all new equipment. It´s like still using floppy disc on the computer, some may do. Who knows? But it´s obsolete, like I think the NPT connection is obsolete.
Figure 48 Figure 49
I know that many will state that we still need the NPT connection. But going to Italy in Erba you will find the manufacturer of figure 48, 49 and 50. If looking at figure 48 you can se a class 150 fitting bolted on flange with the inner check threaded down the inside, all installed on the flange of a three pies valve. Figure 49 illustrates a class 600 lubrication fitting bolted on to a top entry ball valve. In figure 50 the bleeder is also installed by the means of bolts. As you know, we don´t use floppy disc anymore, and there are absolutely no reason for using NPT threads to connect any equipment on high pressure and hydrocarbon equipment, NPT is not good enough in the 21stcentury. That is my personal opinion and I know it´s sheared by many.
To be continued
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