Benoil Services Ltd

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1. STRIPPER RUBBER PACKER INSERTS

a) MATERIAL NOTES

1 Current systems

Upgraded standards offer better wear characteristics and reliability. They have a built-in self-lubrication which reduces frictional wear and start-up jamming. They also have much better tolerance at both low (-50C/-60F) and high (+160C/320F) temperatures. They do not embrittle at the upper limit so that even at excessive temperatures they do not precipitate a catastrophic breakdown. They also do not show any explosive decompression damage at high pressure. These properties are proving so advantageous that the products have gained wide acceptance.
1.1   The 3600 series has improved wear and temperature resistance and replaces others for standard use, including our 3100 series. It is based on a 90A rubber with crosslinking and self-lubrication. For extreme pressures and temperatures, use the 3700 series.
It is recommended for 40C/100F < T < 150C/300F and 2000 < P < 5000psi.
1.2   The 3700 series has extra wear and temperature resistance due to the harder form of the polymer as well as the polymer type and built in lubricating agent. It is for application at extreme pressures and/or temperatures (>4500psi, >150C/300F) instead of the 3600 series. They are not to be expected to be without wear if pushed to say 10,000psi or 160C/320F, but they will wear uniformly, ie safely, if evenly loaded. Because they show no tendency to brittle fracture or explosive decompression, this enables them to be run with confidence. They are, however, designed to be the wearing part of the system and should be checked often when used at extremes. They should always be changed between runs; anything less is a false economy in a high pressure environment.
Though suitable for any operation when T > 100C/212F and P > 3500psi, it becomes essential for T > 150C/300F and P > 8000psi and up to 13000psi.
1.3   A 3800 series is based on a softer rubber (80A) than the 3600 series but, like that series, includes a self-lubricating agent and is cross-linked. It therefore wears rather better than the 3200 and 3500 series. It is expected to serve those applications of low pressure and low temperature where it is desirable that the rubbers be relatively easy to energise. This means that it is believed suitable in VLT use (-50C/-60F) and at the same time serves a higher temperature (+150C/300F) than equivalents of the 3500 series; comment on experience is welcome. It is suitable for 1000psi < P < 4500psi.
1.4   Other developmental series are also available.

b) DESIGN NOTES

1. Sealing Face

We have considered the alternatives to flat sealing faces, which have been promoted (by other suppliers) as giving a more positive seal, evaluating various wavy and toothed interlocks. Although there is an apparent case for supposing that interlock produces a more ready seal, there appear in tests to be no actual sealing benefits over an equivalent size of flat face seal. Also, although the interlock may reduce the chance of ejection of one half when bad wear occurs, we find that a good material will not wear to give this problem anyway. It also appeared that once wear started in an interlock system, it was actually worse on the area near the join. We therefore do not at present list or intend to list such varieties though some might be made available on request.

2. End Face

A further modification has been incorporated into some stripper rubbers; this consists of reinforcing the end faces in order to try to reduce the tendency to wear excessively, which sometimes takes place at the ends causing a funnel shape. We find that a marginal life improvement may indeed be obtained with the standard materials where these are incorrectly used, but that correctly selected and used materials perform well without need of any reinforcement. Also, at elevated temperatures, combination materials have been known to spall apart; the bonding between different materials introduces a complication to the product. As with sealing faces above, we do not at present list a range, but they can be made available.

Feedback on use of rubbers in stuffing boxes is always welcome and any suggestions for improvement will be carefully considered.


c) IDENTIFICATION
Stock is individually labelled and marked with a part number and a batch date. We previously bagged products individually in black plastic as a protection against degradation by air, moisture, heat and light. However, we have also been studying the behaviour of polyurethane products not so protected and have shown that there is no noticeable change of condition over ten years. We therefore decided to discontinue the bagging of packer inserts, with the benefit that products are identifiable at sight.

In the lists, all packers are described with ID / OD / L on OD. The ID corresponds to the CT diameter, and the choice of OD & L depends on the stuffing box to be used. We have sometimes been asked for a comparision of part numbers with competitor products; this is not directly possible, since to state for example that our P/N 1234 was the equivalent of Bowen's 98765 or TOT's 43210 would be inexact. Materials and construction differ, so that exact parallels are unlikely to exist. What matters is the fit in the stuffing box and the functionality of the materials. The differing material performances as tested have been indicated above which is why we offer choices of material.

Not all options are equally recommendable. Thus, a Bowen 4.625 box can be fitted with its 4.625 OD x 3.00 ID energiser and replaceable 3.00 OD rubbers, but it is as well fitted by our 4.625 OD series all-in-one rubbers, which offer the safety benefit of reduced leak paths; Bowen opted for the same design in their second series - our 3679 et seq. The same is true of a TOT 5.50 OD box, where we offer not only the energiser plus 4" OD inserts, but, particularly for the larger CT sizes, all-in-one sets of rubbers.


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