Replacement of V-pack or U-cup Seals With Urethane V-pack Seals
NOTICE P1: "Remove power from the machine" means use the necessary safety procedure for your location. In the USA, this is the OSHA lockout/tagout (LOTO) procedure. More local requirements can also apply. There are replaceable seals just above where the ram shaft comes out of the ram assembly. Usually a small quantity oil escapes past these seals. If the leakage becomes excessive, the seal(s) must be replaced. These seals can be either a V-pack or a single U-cup seal. Replacement with Urethane V- pack seals, explained here, is a relatively simple procedure because the seals are split to wrap around the shaft. V-pack kits are available from from the Milnor Parts department for each ram size. The Urethane V-Pack is thought to be more effective than previous Rubber V-pack or U-Cup.
1. How the V-pack Works
Referring to
Figure 1, the V-pack (1) is a stack of hard urethane seals that wrap around the shaft and fit together in a "V" groove profile. Replacement seals are split. The V-pack fits into a cavity between the shaft (2) and the head gland (3). Most of this cavity is filled by a bronze or steel insert (4). The remaining space is for the seals. A packing gland (5), also called a tension collar, bolted to the head gland controls the V-pack fit. Shim stacks (6) at each bolt position between the head gland and the packing gland must hold the V-pack at a zero clearance fit. The nominal height of the shim stack for a new V-pack for 14, 16, and 18 inch rams is 1/2" (23 mm). The nominal height for the 13 inch ram is 3/8" (9.5 mm). However, V-packs have a large manufacturing tolerance. It is necessary to determine the actual shim stack height based on measurement of your V-pack. Milnor recommends against removal of shims from the shim stack as a way to reduce oil leaks after a V-pack becomes worn. This method risks compression of the V-pack.
Figure 1: V-pack Installed
2. Precautions
This instruction gives the concept of seal replacement, but not a step-by-step procedure. The maintenance can be somewhat different for different field conditions. You must understand hydraulic equipment and be able to apply this information to your specific condition.
WARNING 1 : Crush hazard—You can be crushed by the falling ram. Do this maintenance with the ram and the container (the can) fully down. The diaphragm and the container must rest on the press bed. Do this maintenance with power removed (see Notice P1).
CAUTION 2 : Injury to eyes and skin—Hot hydraulic oil can splash on you Wear eye protection and use care when you open hydraulic lines and remove old seals.
CAUTION 3 : Risk of damage and hydraulic leaks—If the shaft is scored during, or as a result of this maintenance, costly repair or replacement of the ram shaft will be necessary. Avoid any procedure that can cause damage to the shaft surface.
3. Concept of V-pack Replacement
Study Figure 2 and the points given below the figure before you begin the maintenance
Figure 2: V-pack Installation in Progress
Partial Section View
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Legend
- One of two all-thread rods used to lower the packing gland (tension collar).
- New V-pack wrapped around shaft. Stagger splits in adjacent seals 120 to 180° apart.
- Formula to determine required height of shim stack. See A, B, C, and D, below.
- Height of your V-pack. If using red vee packing you must add .080" to the relaxed height. See this article Urethane Vee-Pack for a Single Stage Press
- Height of lip/shoulder on packing gland.
- Height of V-pack cavity.
- Height of shim stack necessary for this V-pack to achieve a zero clearance fit.
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Observe the following points when you do the maintenance:
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- This maintenance is a two person job.
- Use two all-thread rods to lower the packing gland. On large rams, the packing gland weighs approximately 100 pounds (45 kg). Provide 8" (200 mm) minimum work clearance between the head gland and the packing gland.
- Use a seal pulling tool, not air pressure to remove the old seals. New Vee pack kits come with a drill bit for starting a hole in the existing seals. You can use a 3 inch wood screw as a pulling device.
- If the old seal is a U-cup, you will see a UHMW ring pushed out of the seal cavity with the U-cup seal above it. Cut the U-cup seal to remove it. The UHMW ring may be split. If not cut the ring.
- Install the seals with the "V" profile upright, not inverted.
- Stagger the splits between adjacent seals 120 to 180 degrees apart.
- Use the shim stack that gives the V-pack a zero clearance fit; that is, no gaps between seals and no seal compression. Gaps will permit excessive oil to leak. Compression can cause shaft damage and will inhibit ram free fall during operation. V-packs have a large manufacturing tolerance. Measure carefully, as shown in Figure 2, to determine the correct shim stack height to achieve a zero clearance fit. Table 1 gives the two shim sizes available from the Milnor Parts department. Red Vee packing needs additional room to grow in height. See Urethane Vee-Pack for a Single Stage Press
- Push the new seals into the seal cavity slowly and carefully. Make sure that adjacent seals fit together correctly and that no portion of a seal becomes twisted.
- Use the same overall height (thickness) of shim stack at each bolt location to hold the V-pack uniformly around its entire circumference.
- When you re-attach the packing gland (tension collar), tighten the bolts using an alternating pattern. Tighten as specified in document BIUUUM04 “Fastener Torque Requirements” in the service manual.
Table 1: Shims Used on Shaft Seal Tension Collar
Type
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Milnor Part №
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Thickness
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Inch
| Metric |
| Thick | 15U314C | 0.073 | 1.85 mm |
| Thin | 07-10237 | 0.05 | 1.27 mm |
4. Removing Old Seals
The attached instructions suggest using compressed air to remove the seals,
This method may cause more issues than it solves.
Do not use compressed air to remove the old seals from the packing gland
Old seals need to be removed without damaging the cylinder rod. Scores, cuts, and dents can degrade the life of the ram itself. Customers have had success using picks or packing removal tools or the drill bit and wood screw method. Whichever method you choose be sure to keep the rod safe.
NOTE: The instruction attached is for replacing the vee packing when NOT split. This is a much more involved process and is not used if the replacement seals are split. The platen and hub must be removed when installing non-split seals. The instruction below shows those steps.
