Reciprocating Pump Packing Failure 3

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I am looking for some ideas as to why the packing is failing and how long packing on this type of pump in this application should last?
The pump is a Wheatley horizontal quintuplex plunger originally installed in 1983 and replaced in 2004. The original manufactures packing has a 25 day mean time between failures. The Slade brand packing being used since 2002 has a 32 day mtbf. Slade packing consist of braided reinforced graphite. There is no lubrication with this type of packing. The cross section of a ring is square. It has Kevlar fiber corners and 1/8” Teflon spacers for rigidity. When the packing begins to fail we will see an approximately ½” high cone shaped pile of packing material under the packing nut. The plungers will have minimal to no scoring when repacked. They are replaced along with the throat bushings every other failure.
The pump is used to provide seal injection for boiler circulating water pumps. So it runs continuously. Here are the specifications: Speed- 440RPM; Plunger- tungsten carbide, 1.25” bore X 3.5” stroke; Suction- 150deg F, 327psi, dampener charged to 150psi; Discharge- 2900psi, dampener charged to 500psi; Pumped Media- condensate with a chemistry of 3-4ppm silica, 0.1micromhos, 9.1PH, 1.0ppb sodium, 1-2ppb dissolved oxygen.
The manufacture has suggested a spring loaded self adjusting packing that has Kevlar incorporated in the rings. The cross section of a ring is V shaped. This is supposed to be a large improvement over what was originally installed. I do not know why we went to the Slade packing in 2002 over some other choice, other than it is used here successfully on other problem applications for pumps and valves.

 

[PDPumpGuy]

One of the most important, and often neglected, components of a good stuffing box design is the follower ring, or follower bushing. It's the close fitting ring that needs to be installed directly behind the packing on the atmospheric side and in front of the packing nut. It's purpose is to reduce or prevent extrusion of the packing, and that sure sounds like a problem on your application with the 1/2" cone of packing material that balls up under the nut when you have a failure. This ring is often just a copy of the thoat bushing, but needs to fit tight over the plunger, typically in the .005"-.008" range over the OD of the plunger itself.

I'd also make sure you are installing the Slade packing with the actual packing ring, not the Teflon spacer, is against that follower ring.

That said, I would be concerned that solid Teflon spacer rings are probably not appropriate for your application. The relatively high temperatures and pressures would likely cause that Teflon to soften and flow. Carbon filled Teflon spacer rings, Bronze, or even PEEK (overkill) would probably be a better choice.

I think it's reasonable to expect 3-4 months of service life from your packing. You will hear stories of years of service, but your non-lubricated, high pressure, hot water application is pretty tough to achieve those extreme lifes. Be careful about Kevlar. While durable as heck, it is often a lot harder on plungers than many of the other materials. Often, you get longer life on your packing only to trade for shorter life on your plungers, which tend to cost even more to replace.

V style packing can also work well in this application, but I don't know that it will work any better than a good set of braided packing. If you are out of luck with Weathley, then suggest you consult a reputable packing vendor for design assistance such as Utex Industries or CDI Seals, both out of the Houston area.

 

[EVSP9000]

You could look at some of the newer chevron graphite packing materials, i think garlock make one, we have tried them on this type of application with success, but be aware they are very sensitive to installation and loading

Hope this helps

 

[LAsludge]

Thanks guys,
This is the only useful information I’ve been able to find on the subject of packing. Maybe you can educate me a little more. We use a 3 cylinder pump to pressurize our fluid to 12,000 psi. Our packing only lasts about 200 hours. The particulars are as follows:
The fluid is water with 5% solids, 200 cp viscosity, 130 degF, 8.5 PH

On each cylinder we have a 1.25 inch ceramic plunger and the packing from the pressure side to the atmospheric side consists of
1 - loading spring,
1 - metal ring,
5 - Teflon braided packing rings with Teflon separators between rings,
1 - final Teflon separator and
the brass packing nut.
A couple of questions….
1) Why 5 rings? As I understand packing, 5 rings is the minimum but what determines this number?
2) My failures come in two varieties. The first type looks like pieces of packing coming out between the packing nut and the shaft; the second type of failure looks like a bulge on the outer diameter of the last (atmospheric) separator ring.

A little education would be most appreciated.

 

[JakeInApplications]

When using SLADE packing Ive seen that it is usualy best in most applications that only 3 SEALING rings would be used.I would also personally reccomend that when using this brand of packing you would use their spacers with their packing.The reason I say this is their packing needs to be compressed 30% of the stuffing box ,compressing the teflon at the same rate would probablly cause a loss of the lubricants that make the teflon packing so effective.I believe the company makes a style of packing refered to as "CJK"(carbon jacketed) material that they use for shaft stabilization that can be compressed comfortably as the sealing type is which im guessing is the "g" type.By using these in conjunction with each other I have personally seen in pulp and paper where we had a Blow Tank that was impossible to seal which usually lasted about 2 weeks at most (and the shaft was out.150).Using the exact setup as stated above it was sealed for over 18 months and the shaft was actually repositioned back inline.I would call the person that sold you the SLADE material and inquire about your problem or call them direct @ 800-889-6185 where they have some consultants that Ive found are very helpful.Hope this helped out.

 

[ssbb2]

Here is an update. Thanks PDPumpGuy. It was nice to get good impartial information. The Slade vender contacted me several days after I read your input. There application engineer came back with a very similar diagnoses. I was more receptive to there proposal because of the knowledge gained from your input. Jan. 23 we installed a new packing configuration in two of the five stuffing boxes for a test run. The first and last rings were replaced with Vapor deposition graphite (VDG). This is a graphite and SS foil die formed to our stuffing box and plunger dimensions to act as a follower ring. The 1/8” Teflon spacers (S) were replaced with 3/16” carbon filled Teflon. The other rings that were not changed were Graphite foil with Kevlar woven into the corners (K) and Graphite foil (C). All die formed. The set now looks like this: VDG,K,S,C,S,K,VDG. This was installed and tightened very tight with a 16” long spanner wrench. Retightened 1 ½ hours later. Then put in service. 24 hours later we were able to get another ½ turn on the packing nut. It will now be left to run to failure. At the time we retightened the packing. The three with the old configuration were already spitting out packing. The two with the new style were completely clean. Looks promising. The Slade company and vender have been very helpful. I will post another entree when it fails or when we have tripled the life span of the old packing.