D23:
Okay- I wrote the following last week, but now that I’ve come back and read that you’re supplying the water support system for the plan 32… well- that follows the parenthesis.
(I’ll give you the lowdown about shaft sealing. First, choose a pump with a large bore stuffing box. This will make it so much easier to get a seal to work. More room for components, more area for cooling…
I know that several makers of ANSI sized pumps make a vortex generator that is part of the cast of the back-plate that really helps with slurries. Goulds calls it VPI and Flowserve- Durco calls it FML, I think.
If the OEM you like does not there are aftermarket vortex generators that can be installed, Sealmate comes to mind.
Slurry seals get a bad rap. They do. It can be done. If the solids concentration is about 10% or so look into the plain old elastomer bellows pusher seals with hard face materials, ex, John Crane Type 1, Flowserve Pac Seal… These work famously, a single spring won’t clog easily, the elastomer bellows holds up well in slurries too. If the solids content is higher there are two other types to look into, metal bellows seals, or the seals touted as slurry seals.
Metal bellows seals work well because the edges of the bellows “knife” through the solids, and windage is created around the bellows helping to increase flow around the seal as the bellows rotates. Metal bellows seals also have the advantage of a stationary secondary seal element. The o-ring doesn’t have to move, so no O-ring hang-up.
The seals promoted as slurry seals are generally made to work with the special stuffing boxes listed above. These designs generally use a stationary O-ring to wipe against the seal face to exclude solids from the springs that move this same seal face. The seals are made with a profile that tries to create a smooth flat profile around the faces to minimize the turbulence around the faces and reduce the chances that they’ll be abraded. This is partly why they are designed to work without a flush.
A Plan 32 Flush with a throat bushing is the easiest way to make a seal work in a slurry service. The flush rate is adjusted to cool the faces with clean fluid and to create enough pressure and flow through the stuffing box and the bushing to exclude the abrasives. Heck, the bushing is a plus if your bearings ever go to pot. Hard faces are a must; the solids can be crushed and spat out the atmospheric side. If you are really concerned, a Plan 62, or quench can be used to both cool the seal faces from the atmospheric side, and flush solids away from the faces.
If the solids are heavy enough and you want to try, a Plan 31 is the use of a cyclone separator off the discharge, with the clean fluid to the stuffing box, and the dirty fluid back to suction. These can be tricky, because they have to be “tuned”, the losses through the tubing have to be considered for these to work best. Cyclones can also plug and be a real pain in the keester.
I’ve just had really good experience with a double metal bellows seal in service at a Calcium Chloride unit. A Galagher pump with a stuffing box that used to be packed with aramid packing, a lantern ring, and what the other vendor called an excluder packing ring (just a solid teflon packing ring cut on a bias so it closes in on itself as you tighten the packing gland- a bushing). The pump pulls the “mud” from the bottom of a clarifier and sends it to a filter press. We installed this back to back metal bellows seal with a modified plan 52, or a 54, plant water piped in to the area between the seals at 20 or so pounds above the stuffing box pressure and back out to the sewer. This thing has run like a champ.)
Now for the rest-
What is the current configuration? If the water is clean I suppose the problem is keeping it at a constant pressure or at the pressure required to exclude the slurry from the stuffing box. Consider some kind of accumulator or N2 bottle system to boost the pressure with a regulator. I know that at least one company offers what looks like a reservoir, but has a disc and rod so that on one side of the disc the reservoir is at the discharge pressure, and the other side, due to the difference in area of the disc because of the rod (Pressure= Force/Area), is at some constant ratio higher. (check this link out-
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If the pressure isn’t the issue, what is?
Josh
p.s.- Just remember that the Venezuelans are having their own problems with strikes and politics too. And even if they do get past those issues and boost production, Venezuelan crude is higher in Sulfur. More of that means more maintenance, more down time, and decreased profit margins.
