Nas 1638 Pdf
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Encoding method of the level of contamination based on the number of particles per unit of volume divided into size classes. Standard NAS 1638 is still used, yet due to the fact that by now it is considered obsolete, it has been replaced by standard AS4059 / ISO 4406 that concerns the encoding of the level of contamination of a fluid. In a hydraulic system, the fluid re-circulates and tends to reach a stable level of contamination over time, that reflects the characteristics of the type of filter used. The sizes of the particles of interest will be those appropriate to the power of removal of the filter.
In standards NAS 1638 and AS4059E, the particles are grouped into intervals as per size: between 5 and 15 µm, between 15 and 25 µm, between 25 and 50 µm, between 50 and 100 µm and, finally, over 100 µm. A class identification is attributed to each of these ranges of values, based on a numerical comparison of the particles present with a standardised table.
Standard NAS 1638 has been developed in order to define the levels of contamination in the aerospace sector. Standard NAS 1638 has been replaced by standard AS4059, the E version of which has been adapted so as to provide data on the levels of contamination for both cumulative and differential values.
National Aerospace Standard (NAS) 16381 is a particulate contami-nation coding system used in the fluid power industry to simplify the commu- nication of data from particle counters. It converts the particle counts at various size ranges into convenient broad-base classes. The particle numbers can range from single particles to many millions; therefore, a power series is used to cover the number range with a convenient number of classes.
NAS 1638 was conceived in the 1960s to control the amount of contamination delivered in aircraft hydraulic components, and became an American National Aerospace Standard in 1964. No coding system existed at the time for completed systems, so it was logical that it would be applied in this area.
NAS 1638 saw widespread acceptance in the 1970s and 1980s by industries where reliability was a prerequisite, in areas such as offshore oil production, iron and steel industries, etc. It led to the development of other coding systems, the most notable being the International Organization for Standardization (ISO) 44062.
This is a result of recent changes to the ISO contamination standards for automatic particle counter (APC) calibration3, which necessitated the review of NAS 1638 and resulted in its withdrawal for newly designed systems.
NAS 1638 was the forerunner of other contamination coding. The concept of the code can be seen in Table 1 and it is based upon a fixed particle size distribution of the contaminant over a size range of >5 to >100 µm. This distribution was based on particle contamination inside delivered aircraft hydraulic components in the 1960s.
Since its inception in the 1960s, the use of finer rated filters in hydraulic systems meant that the distribution of particles did not follow NAS 1638 as the proportion of larger particles (>15 µm) was reduced through filtration. These relative low numbers generated significant errors in data at the larger sizes (>25 µm) due to the use of bottle samples5.
Another criticism of NAS 1638 was that there was little guidance on how to use or apply it. For this reason, and to generally improve the standard, the SAE A6 Aerospace panel developed AS40596 for aircraft hydraulic systems. This subsequently became de facto ISO 11218. Few aircraft companies adopted this standard, and very few industrial companies even knew it existed despite the fact that it overcame the deficiencies of NAS 1638.
Notice that the same particle numbers are used in AS4059 as NAS 1638 (to verify this try subtracting the >15 from >5 µm numbers and comparing it with the 5 to 15 µm in NAS 1638). In the transition period, the standard applies to both methods of calibration of APCs (ISO 4402 and 11171).
Many are specified for analyzing oil samples and presenting data to NAS 1638 format for existing designs. The reasoning behind this is not entirely clear, but thought to be to separate old and new APC data. APC users are recommended to switch to the new standards.
In Table 3 it can be seen that the particle counts are defined by a number (relating to the quantity of particles) and a letter (relating to the size). This concept gives AS4059 much more flexibility than was possible with NAS 1638 because it is often the control of the cleanliness level that specifiers require rather than a fixed distribution; for example, they can specify improved control over critical sizes or relax controls over those that are not. Equally, sizes that are not critical can be omitted. There are three reporting options:
Is NAS 1638 dead? Well . . . not quite. NAS 1638 can be used for existing systems where correlation with earlier data is necessary. However, users are encouraged to change to AS4059 as soon as possible so that everyone is speaking the same language.
Current specifications, like those based on a single number, for instance NAS 1638 Class 6, can be swapped to AS4059 Class 6B through F to provide the same control over the 5 to 100 µm-size range, or perhaps even updated to reflect current and modern requirements. Although the current version of AS4059 allows two methods of calibrating APCs, the use of ISO 11171 is recommended as it gives improved precision.
One aspect of the change, which may be a little unclear, is that of component cleanliness - the scope of the original NAS 1638 document. As NAS 1638 is inactive for new components/systems, and AS4059 was developed for hydraulic systems, how is the cleanliness of components defined? The Society of Automotive Engineers (SAE) Committee has been made aware of this and is deliberating. The author recommends the use of AS4059 system for commonality using sizes B to F, and relating the particle counts to 100 mL of the components wetted volume.
Another aspect that is giving rise for concern is the statement in clause 6.1.3 that forbids the use of APCs with NAS 1638. This is in spite of cleanliness specifications being written around them. The reason for this is not entirely clear but it is thought to be the need to separate old and new APC data. APC users are recommended to switch to the new AS4059 standard.
NAS 1638 is an older standard developed in 1964 to define classes of contamination in aircraft components and hydraulic fluids. The classes refer to maximum number the particles in 100mL in different size classes. The table below shows the classification values that may still be in use for older specifications based on Hiac particle counters, but this standard officially became invalid in 2001. Most users use a single code number based on the highest particle count in any of the size bins.
NAS 1638 was first issued in 1964 to provide a means to control the amount of contamination delivered in aircraft hydraulic components. The standard contains a series of 14 classes covering very clean to very dirty levels, where the interval between each class is double the contamination level. This principle is a feature of many of the classes in more recently developed standards, such as the AS 4059 (adopted as ISO 11218).
The replacement AS 4059 defines cleanliness classes for particulate contamination of hydraulic fluids and includes methods of reporting related data. Conversion from NAS 1638 cleanliness class specifications to AS4059 class specifications is defined and the differences explained. This document is preferred because of the versatility in identifying a maximum class in multiple size ranges, the total number of particles larger than a specific size or designating a class for each size. FYI: NAS 1638 classes based on weight of particles are not applicable to either of these classes and are not included.
Measuring hydraulic cleanliness is not straight forward, consequently various standards exist on this subject. The two most likely to be encountered in the oil & gas, and process industries are The ISO Cleanliness Code (ISO 4406), and The NAS 1638 cleanliness standard.
The NAS 1638 cleanliness standard was originally developed for aerospace components in the US but is still widely used for industrial and aerospace fluid power applications. It is used widely in the UK North Sea industries. NAS1638 is comprised of fluid cleanliness classes, each class defined in terms of maximum allowed particle counts per 100ml for designated particle size ranges. See the NAS 1638 chart below for the various cleanliness levels:
Độ sạch của dầu thủy lực cần được theo dõi để duy trì các thành phần của hệ thống thủy lực ở mức cho phép. Nhiều tổ chức quốc gia và quốc tế như ISO, SAE, Tiêu chuẩn Hàng không Vũ trụ Quốc gia (NAS), v.v., đã phát triển các tiêu chuẩn để xác định phân loại kích thước hạt và nồng độ ô nhiễm trong dầu thủy lực. Tất cả các tiêu chuẩn đều quy định mức độ nhiễm bẩn tính theo số đếm trên một thể tích chất lỏng và cung cấp các phương pháp dễ dàng để chuyển đổi số lượng hạt thành các giới hạn dễ hiểu. Bài viết này chúng ta cùng tìm hiểu về tiêu chuẩn ISO 4406 và NAS 1638 về độ sạch dầu thuỷ lực.
Tiêu chuẩn ISO 4406 và NAS 1638 về độ sạch dầu thuỷ lực được đưa ra bởi 02 Tổ chức là: Tiêu chuẩn Hàng không Vũ trụ Quốc gia (NAS) 1638 và Tổ chức Tiêu chuẩn Quốc tế (ISO)
Tiêu chuẩn về độ sạch của NAS 1638 ban đầu được phát triển cho các bộ phận hàng không vũ trụ ở Mỹ nhưng vẫn được sử dụng rộng rãi cho các ứng dụng năng lượng chất lỏng trong công nghiệp và hàng không vũ trụ. Nó được sử dụng rộng rãi trong các ngành công nghiệp Biển Bắc của Vương quốc Anh. NAS1638 bao gồm các cấp độ sạch chất lỏng, mỗi cấp được xác định theo số lượng hạt tối đa cho phép đối với các phạm vi kích thước hạt được chỉ định. Xem biểu đồ NAS 1638 bên dưới: 2b1af7f3a8