Figure 1-1 Typical oil burner fuel pump shaft seal
lip type seal with a metal casing . The seal is pressed into to pump body during manufacture and is not practically field-replaceable .
In legacy heating systems , the dominant seal material is nitrile-acrylonitrile butadiene rubber or NBR ; an unsaturated copolymer constructed of acrylonitrile and butadiene monomers . The presence of the acrylonitrile monomer imparts permeation resistance characteristics to a wide variety of solvents and chemicals , while the butadiene component in the polymer contributes toward the flexibility . Like any given polymer , the mechanical properties of nitrile vary depending on its constituents . Differences in composition may be based on the acrylonitrile content used in synthesis ( commercial nitrile rubber can vary from 25 % to 50 %), reinforcement fillers , plasticizers , antioxidants , processing aids , and cross-linking agents . In the process of obtaining a listing approval for a burner for application in this market , testing is typically done , guided by Standard UL 296 which effectively incorporates material compatibility tests for elastomeric materials , UL 157 . This test involves an immersion period of 70 hours at 23 ± 2 ° C ( 73 ± 3.6 ° F ).
Suitable elastomers are required to retain more than 60 % of their unconditioned tensile strength and elongation and volume swell must fall within the range of -1 to + 25 %. Generally , nitrile materials have good resistance to petroleum products and are commonly used with heating oil applications . The chemical resistance , however , of nitrile to biodiesel fuel or biodiesel / heating oil blends was not as well established . There are nitrile materials offered commercially which are at least nominally compatible with biodiesel blends to the B-100 level .
In a study published in 1997 Southwest Research Institute reported on their evaluation of a range of different elastomer types exposed to biodiesel / petroleum blends . Fuels included in this study included JP-8 , B-100 , low-sulfur diesel fuel , “ reference ” diesel fuel and blends at the B-20 and B-30 level . Samples were immersed at 51.7 ° C ( 125 ° F ) for 0 , 22 , 70 , for 694 hours .
Tests reported in the study by Southwest Research Institute showed a notable effect of the biodiesel blend on the nitrile materials . This included volume swell in the 20 % range and a reduction in tensile strength as high as 38 %. These tests were done prior to the implementation of oxidation reserve specifications and the lowering of the acid value specification for B100 , and at higher temperature and for much longer times than required by UL 157 . Even so , the magnitude of property change reported is within the
28 FEBRUARY 2019 | FUEL OIL NEWS | www . fueloilnews . com acceptable range under UL 157 , although marginally .
In a more recent study Southwest Research Institute and the National Renewable Energy Laboratory evaluated the compatibility of several elastomers including three different types of nitrile in B20 blends and ethanol-diesel blends . The nitrile materials included a general purpose NBR , and high aceto-nitrile content rubber , and a peroxide-cured nitrile rubber . These materials were selected as being typical of materials used in automotive applications . Samples were immersed at 40 ° C ( 104 ° F ) for 500 hours .
Tests reported in the earlier study by Southwest Research Institute for elastomers common to diesel engines showed some effect of the biodiesel blend on the nitrile materials . This included volume swell in the 20 % range and a reduction in tensile strength as high as 38 %. The later study reported on by SwRI and NREL showed no significant effect of the biodiesel blends on the NBR 1-6 materials studied , leading to the conclusion “ all of these elastomers appear to be fully compatible with 20 % biodiesel blends .”
In another , potentially relevant study done by Underwriters Laboratories the compatibility of B5 blends with elastomers typically used in oil burner applications was studied in compliance with the UL157 standard . Two specific nitrile materials were included . This study showed no significant effect of the biodiesel blend on the materials tested . The goal of the work done in this project was to extend the prior NBR elastomer studies on biodiesel compatibility to the entire range from B0 to B100 and to focus specifically on the NBR material used in legacy pump shaft seals in oil burner pumps . This specific component was selected cooperatively with equipment manufacturers as potentially the most vulnerable part of existing systems .
A key question for this study was the “ limit value ” i . e . the maximum amount of biodiesel that could be used in a legacy system at least based on this one specific metric . The experimental work reported in this section was done by Dr . Chad Korach and Richard Anger at the State University of New York at Stony Brook under contract to BNL , as part of this project .
In this study the impact of biodiesel at a wide range of blend levels was evaluated for the nitrile material commonly used on legacy oil burner pumps in the U . S . Sheets of the nitrile material were obtained with assistance from the Suntec Corporation . The specific material is grade A795 NBR from the NOK corporation . Samples of this material were cut into standard dog bone shapes as well as circles and rectangular shapes . Immersion with different biodiesel / No . 2 oil blends was done for 670 hours at 51.7 ° C ( 125 ° F ).
After immersion , all samples were removed from the oil , cleaned , and then subjected to nondestructive hardness and swell measurement tests prior to the destructive tensile or compression set tests . The cleaning process consisted of a ~ 3 second acetone dip to remove residual oil , and blotting with laboratory tissues to dry . All samples , both discs and dog bone specimens , were used to measure the volume swell and hardness ; dog bone samples only were used to measure tensile strength ; and the disc samples only were used to measure the compression set of the materials . The biodiesel fuel used in this effort was a commercial sample , received from Hero BX , Erie Pa . The No . 2 fuel oil used was also a commercial sample , obtained locally .
When biodiesel degrades during extended storage , one possible
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