To keep less than perfectly matched mating surfaces from leaking it is always a sound idea to use rubber gaskets and gasket seals. The commonest usage of rubber gaskets is in the covering lid of the domestic pressure cookers. However, gaskets manufacturers cater to the industrial market as much as to the domestic one. This is because seals and gaskets are needed to keep uneven machinery edges running smoothly.
Gaskets are made of not simply rubber, but also of sponge, cork, neoprene, graphite, asbestos (not a preferred option because of the health hazards it can cause) fiber and foam. Typically gasket seals are needed to seal in gases/moisture from escaping or entering. In conventional gaskets, as the flange fasteners are tightened, the flange deflects radially under load, resulting in the greatest gasket compression, and highest gasket stress, at the outer gasket edge. Since the carrier ring used in gasket seals take this deflection into account when creating the carrier ring for a given flange size, pressure class, and material, the carrier ring profile can be adjusted to enable the gasket seating stress to be radially uniform across the entire sealing area.
If you need to place orders with a gasket manufacturer, apart from taking into account their track record and experience, you also need to check whether they can supply seals and gaskets in a variety of materials. The kind of material to be used will be defined by the kind of load the gasket needs to take, probable chemical reactions as well as budgetary constraints. Rubber gaskets and gasket seals made of neoprene offer greater degree of tensility and heat resistance, with neoprene taking an edge in matters of heat resistance.
If you need double-jacketed gaskets, they are a combination of filler material and metallic materials. A tube with ends that resemble a ‘C’ is made of the metal with an additional piece made to fit inside of the ‘C’ making the tube thickest at the meeting points. The filler is pumped between the shell and piece. They are best used for insulation purposes. Clifton rubber is the largest manufacturer of rubber products like rubber mouldings, rubber gaskets & extrusions.
Posts tagged ‘Proof’
In 2006, results from the world’s largest low fat diet project were published (see reference at end). This was a US government-funded study of 48,835 postmenopausal women in a multicenter prospective, randomized clinical trial known as the Women’s Health Initiative Randomized Controlled Dietary Modification Trial. The study was conducted from 1993 to 2005 at 40 centers around the country. The volunteers were randomly assigned to either a low-fat diet group (19,541 women) or a regular diet group (29,294 women). After about eight years of follow-up, this large and costly study did not find any significant differences in breast cancer incidence between postmenopausal women who were asked to eat a low-fat diet and those who continued to eat their regular diet. On the other hand, the results did suggest that changing to a low-fat diet may reduce the risk of breast cancer for women who had diets very high in fat to begin with.
According to most experts, the following may be reasons why this study showed no significant benefit:
1) Not many women met the 20% fat intake goal. This “low-fat diet” regimen may not have truly been low in fat. Since most women did not meet the fat-reduction goal, this study may have proven only that the approach to the intervention did not work. It did not prove that a truly low-fat diet doesn’t help protect you from breast cancer. Getting only 20% of your calories from fat is very difficult to do. This means that, if you eat 2,000 calories per day, only 400 calories could come from fat. So it’s not surprising that less than a third of the women met this goal after the first year, and only 14% continued to meet the goal after six years. Because so few women met the requirements of the study, it means that we don’t really know how a diet low in fat affects breast cancer risk.
2) Diets were self-reported and infrequent, which may make them unreliable. This study relied on the women’s written reports of what they ate, which may not be an accurate reflection of true intake. These reports were done occasionally. No daily food log or journal was done and checked. Most of us aren’t proud to admit in an interview or questionnaire that we’ve broken the rules and haven’t stuck to the “prescribed diet.” So there may be a tendency to under-report the amount of fat actually eaten.
3) Other changes besides the low-fat diet. The study did not separate out the effects of reducing the amount of fat eaten vs. the effects of increasing fruit and vegetable servings. Women in the low-fat diet group ate almost two more servings per day of fruits and vegetables than women in the regular diet group and about one more serving of grains.
4) Length of follow-up time. While 48,835 women is a lot of people, eight years isn’t a lot of follow-up time. Eating a low-fat diet for 15 or 20 years may offer more significant benefits and show a closer relationship between dietary fat and breast cancer risk.
5) Baseline body mass index. In this study, 74% of the women were classified as overweight by body mass index at the beginning of the study. So we don’t really know if a low-fat diet would offer benefits to women who are at a normal weight to begin with.
6) All the women were postmenopausal. It may be that dietary fat plays a more important role in the diets of younger, premenopausal women. It makes sense that your diet in the first 50 years of your life might affect your cancer risk in the second half of your life. This study doesn’t address that question.
7) The type of fat wasn’t specified. There are three basic types of fats: saturated, mono-unsaturated, and poly-unsaturated. In this study, women were asked only to reduce fat. They weren’t asked to consider the various types of fat or told that reducing saturated fats may offer more health benefits than reducing unsaturated fats. Saturated fats are only found in foods that come from animals and are the types of fats that raise your blood cholesterol level. Trans fats (also called trans-saturated fats) are man-made fats. (Vegetable oils are modified to form margarine and vegetable shortening, both of which are trans fats.) Trans fats also are added to prepackaged foods. Saturated fats raise your blood’s “bad” cholesterol (low-density lipoprotein or LDL) level and lower your “good” cholesterol (high-density lipoprotein or HDL) level. Mono-unsaturated and poly-unsaturated fats are found in plant foods like vegetables, nuts, and grains, as well as oils made from these nuts and grains (canola, corn, soybean). Omega-3 and omega-6 fatty acids are poly-unsaturated. Besides vegetables, nuts, and grains, omega-3 and omega-6 fatty acids are also found in coldwater fish such as tuna, salmon, and mackerel. Some studies have shown that eating foods that have mono- or poly-unsaturated fats can help reduce your levels of “bad cholesterol.” Mono- and polyunsaturated fats may also keep your triglyceride levels low. Triglycerides are a form of fat in your bloodstream.
None of the women in either group were asked to change their health-related behaviors, such as exercise, drinking or smoking. These known risk factors for breast cancer were left uncontrolled and may obscure any benefit from eating less fat.
9) This study is about a low fat diet; it is not about going from an overweight/obese state to a normal weight. Eating less fat while staying persistently fat may not help anyone! Since this study cost nearly half a billion dollars, it is unlikely that another lifestyle intervention clinical trial at this large scale would be done again anytime soon, particularly in the current US economy.
Reference: Prentice RL, et al. Low-fat dietary pattern and risk of invasive breast cancer: the Women’s Health Initiative Randomized Controlled Dietary Modification Trial. Journal of the American Medical Association, volume 295, pages 629-42, 2006.
