ASTM F1791-00(2019)

Standard Specification for Filters Used in Air or Nitrogen Systems

ABSTRACT
This specification covers the design, construction, test, and performance requirements for air or nitrogen system filters, referred to hereinafter as filters. These filters are intended to be installed in-line to protect equipment from particular contamination. Filter element type: type 1 - disposable, and type 2 - cleanable. Filter element bypass composition - composition A - with bypass, and composition B - without bypass. Filter element differential indicator style: style I - with differential pressure indicator, and style II - without differential pressure indicator. Visual examination, hydrostatic shell test, external leakage test, and bubble point test shall be performed to meet the requirements prescribed.
SCOPE
1.1 This specification covers the design, construction, test, and performance requirements for air or nitrogen system filters, referred to hereinafter as filters. These filters are intended to be installed in-line to protect equipment from particular contamination.  
1.2 The values stated in SI units are to be regarded as standard. The values given in parentheses are mathematical conversions to inch-pound units that are provided for information only and are not considered standard.  
1.3 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 30-Apr-2019
• ICS: 13.040.40 - Stationary source emissions
• Technical Committee: F25 - Ships and Marine Technology
• Drafting Committee: F25.11 - Machinery and Piping Systems

Relations

• Replaces: ASTM F1791-00(2013) - Standard Specification for Filters Used in Air or Nitrogen Systems
• Effective Date: 01-May-2019
• Refers: ASTM F992-86(2011) - Standard Specification for Valve Label Plates
• Effective Date: 01-Apr-2011
• Refers: ASTM F992-86(2006) - Standard Specification for Valve Label Plates
• Effective Date: 01-Feb-2006
• Refers: ASTM F992-86(2001) - Standard Specification for Valve Label Plates
• Effective Date: 27-Mar-1986

Overview

ASTM F1791-00(2019), Standard Specification for Filters Used in Air or Nitrogen Systems, defines the requirements for design, construction, testing, and performance of in-line filters intended to protect equipment by removing particulate contamination from air or nitrogen systems. Developed by ASTM Committee F25 on Ships and Marine Technology, this standard promotes quality and safety for industrial, maritime, and process applications requiring clean and reliable air or nitrogen supply.

ASTM F1791 outlines specifications for two filter element types (disposable and cleanable), as well as versions with or without bypass features and differential pressure indicators. It covers various pressure ratings, sizes, and end connections to ensure proper installation and performance across diverse system designs.

Key Topics

• Design and Construction Requirements

  • Filters must be built from corrosion-resistant materials suitable for air or nitrogen lines.
  • Options include bolted flanged body and bowl for easy maintenance.
  • Elements must be reliably fixed in place to prevent misalignment.

• Filtration Performance and Ratings

  • Contaminant removal ratings are specified as nominal or absolute, ensuring effective particulate removal.
  • Pressure ratings are standardized, with filters classified by nominal pipe size and maximum allowable working pressure.
  • Options for cleanable or disposable elements are available to suit maintenance needs.

• Bypass and Differential Indicator Features

  • Filters may be supplied with (Composition A) or without (Composition B) a bypass option for flow continuity in case of blockage.
  • Styles include options with (Style I) or without (Style II) a built-in differential pressure indicator to signal filter service needs.

• Testing and Quality Assurance

  • Mandatory evaluations include visual examination, hydrostatic shell tests, external leakage tests, and bubble point tests for filter element integrity.
  • Each filter must demonstrate bubble-tight sealing and meet contaminant retention criteria.
  • Manufacturers must adhere to documented quality assurance systems for ongoing compliance.

Applications

• Industrial and Process Systems

  • Essential for pneumatic and nitrogen systems in manufacturing facilities to prevent equipment fouling, wear, and unplanned maintenance.

• Marine and Shipboard Equipment

  • Designed to comply with stringent vibration, shock, and environmental requirements, making them suitable for shipboard use and other mobile platforms.

• Laboratories and Analytical Installations

  • Protects sensitive instruments from particulate contamination, safeguarding the accuracy and reliability of analysis and measurements.

• Compressed Air and Gas Networks

  • Maintains cleanliness in air compression and nitrogen distribution pipelines to minimize risks of downstream contamination.

Related Standards

• ASTM F992
  Specification for Valve Label Plates-Referenced for identification plate requirements.

• ASME B16.11/B16.25/B16.34
  Standards for forged fittings and pressure-rated pipe connections, applicable for filter end connections.

• MIL-STD-167-1, MIL-STD-740-1, MIL-S-901
  U.S. military standards for vibration, noise, and shock testing of shipboard equipment.

• SAE ARP 901
  Aerospace practice for bubble-point test methods-crucial for verifying filter element integrity.

• MIL-F-1183, NAVSEA Drawings
  Used for further defining end connections and construction requirements in military and naval applications.

Practical Value

ASTM F1791-00(2019) provides comprehensive criteria for the selection, installation, and maintenance of inline filters in air and nitrogen systems. By following this standard, designers, OEMs, and maintenance teams can ensure reliable filtration, extended equipment life, and reduced service interruptions. The classification of filter types, bypass options, and indicators empowers users to tailor solutions to safety requirements, maintenance cycles, and system criticality.

Keywords: air system filters, nitrogen system filters, ASTM F1791, in-line filters, particulate filtration, equipment protection, industrial filtration standards, filter testing, quality assurance, maintenance.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation:F1791 −00 (Reapproved 2019) An American National Standard
Standard Specification for
Filters Used in Air or Nitrogen Systems
This standard is issued under the fixed designation F1791; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2.4 Military Standards and Specifications:
MIL-STD-167-1 Mechanical Vibrations of Shipboard
1.1 This specification covers the design, construction, test,
Equipment (Type I—Environmental and Type II—
andperformancerequirementsforairornitrogensystemfilters,
Internally Excited)
referred to hereinafter as filters.These filters are intended to be
MIL-STD-740-1 Airborne Sound Measurements andAccep-
installed in-line to protect equipment from particular contami-
tance Criteria of Shipboard Equipment
nation.
MS16142 Boss, Gasket Seal Straight Thread Tube Fitting,
1.2 The values stated in SI units are to be regarded as
Standard Dimensions for
standard. The values given in parentheses are mathematical
MIL-S-901 Shock Tests, H.I. (High-Impact); Shipboard
conversions to inch-pound units that are provided for informa-
Machinery, Equipment and Systems, Requirements for
tion only and are not considered standard.
MIL-F-1183 Fittings, Pipe, Cast Bronze, Silver-Brazing,
1.3 This international standard was developed in accor- General Specifications for
dance with internationally recognized principles on standard-
2.5 Naval SEA Systems Command (NAVSEA)—Government
ization established in the Decision on Principles for the
Drawings:
Development of International Standards, Guides and Recom-
NAVSEA 803-1385884 Unions, Fittings and Adapters Butt
mendations issued by the World Trade Organization Technical
and Socket Welding 6000 PSI, WOG, NPS
Barriers to Trade (TBT) Committee.
NAVSEA 803-1385943 Unions, Silver Brazing 3000 PSI,
WOG, NPS, for UT Inspection
2. Referenced Documents
NAVSEA 803-1385946 Unions, Bronze Silver Brazing,
2.1 ASTM Standards:
WOG for UT Inspection
F992 Specification for Valve Label Plates
3. Terminology
2.2 American Society of Mechanical Engineers (ASME):
B1.1 United Screw Threads (UN and UNR Thread Form)
3.1 Definitions:
B1.20.1 Pipe Threads, General Purpose, Inch
3.1.1 absolute contaminant removal rating, n—the smallest
B16.11 Forged Fittings, Socket-Welding and Threaded
size of contaminant as defined in ARP 901 that the filter will
B16.25 Buttwelding Ends
retain with 100 % efficiency by weight.
B16.34 Valves Flanged, Threaded, and Welding End
3.1.2 bubble point, n—the pressure differential across a
2.3 Society of Automotive Engineers (SAE):
submerged filter element required to produce a visible and
ARP 901 Aerospace Recommended Practice—Bubble-Point
steady stream of air bubbles. Correlation between bubble point
Test Method
and contaminant removal capability provides an economical
means to test for contaminant removal capability on a produc-
tion basis. The bubble point indicates the maximum pore size
This specification is under the jurisdiction of ASTM Committee F25 on Ships
of the filter media under static conditions.
and Marine Technology and is the direct responsibility of Subcommittee F25.11 on
Machinery and Piping Systems.
3.1.3 bubble-tight, n—no visible leakage over a 3-min
Current edition approved May 1, 2019. Published June 2019. Originally
period using either water submersion or the application of
approved in 1997. Last previous edition approved in 2013 as F1791 – 00 (2013).
bubble fluid for detection.
DOI: 10.1520/F1791-00R19.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
3.1.4 clean filter element pressure drop, n—the pressure
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
drop across the filter element when it is new or uncontami-
Standards volume information, refer to the standard’s Document Summary page on
nated.
the ASTM website.
Available from American Society of Mechanical Engineers (ASME), ASME
International Headquarters, Two Park Ave., New York, NY 10016-5990, http://
www.asme.org.
4 5
Available from SAE International (SAE), 400 Commonwealth Dr.,Warrendale, Available from DLA Document Services, Building 4/D, 700 Robbins Ave.,
PA 15096, http://www.sae.org. Philadelphia, PA 19111-5094, http://quicksearch.dla.mil.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F1791−00 (2019)
3.1.5 cleanable filter element, n—a filter element that, after “built-in” contamination, such as, welding scale, metal
being contaminated to its dirt-holding capacity (contaminated particles, or air-borne dust combined with the media during its
filter element pressure drop), can be restored by cleaning to manufacture, to leave the filter and shed or migrate into the
operational condition and with a pressure drop not exceeding flow stream.
the required clean filter element pressure drop.
3.1.22 nominal contaminant removal rating, n—thesmallest
3.1.6 contaminant removal rating, n—this is a measure of size of contaminant as defined in ARP 901 that the filter will
retain with 98 % efficiency by weight.
the size of contaminants that the filter can remove from the
flow stream.
3.1.23 operating pressure, n—the pressure within the filter
during service.
3.1.7 contaminated filter element pressure drop, n—the
pressure drop across the filter element when it is contaminated
3.1.24 pressure ratings, n—the pressure rating of the filter
to the point where cleaning or replacement is required.
shall be defined in the documents listed in Table 1. The
pressure rating for a filter is the maximum allowable working
3.1.8 differential pressure indicator actuation pressure,
(service) pressure at 100°F (38°C).
n—the pressure drop across the filter element at which the
differential pressure indicator actuates.
4. Classification
3.1.9 disposable filter element, n—a filter element that, after
4.1 Filters shall be of the following types, compositions,
being contaminated to its dirt-holding capacity (contaminated
styles, pressure ratings, sizes, end connections, and contami-
filter element pressure drop), cannot be restored to operational
nation removal ratings, as specified in Section 5.
conditions and thereafter should be replaced.
4.1.1 Filter Element Type:
3.1.10 external leakage, n—leakage that escapes to atmo-
4.1.1.1 Type 1—Disposable.
sphere.
4.1.1.2 Type 2—Cleanable.
3.1.11 filter element bypass full-flow differential pressure,
4.1.2 Filter Element Bypass Composition:
n—the pressure drop across the filter element at which the filter
4.1.2.1 Composition A: with bypass.
bypass is passing the full-flow rating of the filter.
4.1.2.2 Composition B: without bypass.
4.1.3 Filter Element Differential Indicator Style:
3.1.12 filter element bypass reseat differential pressure,
4.1.3.1 Style I: with differential pressure indicator.
n—the pressure drop across the filter element at which the filter
4.1.3.2 Style II: without differential pressure indicator.
bypass reseats after passing the full-flow rating of the filter.
4.2 Pressure Ratings—Filters shall have pressure ratings
3.1.13 filter element bypass set differential pressure, n—the
selected from those listed in Table 1 and specified in Section 5.
pressuredropacrossthefilterelementatwhichthefilterbypass
The pressure rating selected shall be the same for both the filter
opens.
inlet and outlet.
3.1.14 filter element collapse strength—the maximum pres-
1 1
4.3 Size—Filter sizes shall be ⁄4 NPS (13.5 mm), ⁄2 NPS
sure drop or differential across the filter element that the
3 1
(21.3 mm), ⁄4 NPS (26.9 mm), 1 NPS (33.7 mm), 1 ⁄4 NPS
element must withstand without collapse, damage, or impair-
ment of performance capabilities.
3.1.15 filter element contaminant-holding capacity, n—also TABLE 1 Filter Inlet and Outlet End Connections
commonly termed “dirt capacity.” The amount of a
Applicable Documents
Type of End for Dimensional
contaminant, expressed in weight, that the element can hold
Pressure Rating
Connection Details of
when its resistance to flow causes a pressure drop equal to the
End Connections
contaminated filter element pressure drop.
Butt-welded ASME B16.34 Class 150, ASME B16.25
300, 400, 600, 900,
3.1.16 filter element pressure drop, n—the pressure drop
1500, 2500, or 4500
across the filter element.
Socket-welded ASME B16.34 Class 150, ASME B16.11
300, 400, 600, 900,
3.1.17 filter housing pressure drop, n—the pressure drop
1500, 2500, or 4500
accounted for by the filter housing.
Threaded (tapered ASME B16.34 Class 150, ASME B1.20.1 and
pipe thread) 300, 400, 600, 900, ASME B16.11
3.1.18 filter pressure drop, n—the pressure drop across the
1500, or 2500
A
entire filter (element and housing) at any given flow rate of the
Union-end, MIL-F-1183 (O-ring type) MIL-F-1183 (O-ring
2 2
silver-brazed
400 lb/in. (2.758 type) 400 lb/in.
service fluid (air or nitrogen).
MPa) (2.758 MPa)
A
3.1.19 flow capacity, n—the maximum flow rate that the
Union-end, 803-1385946 1500 803-1385946 1500
2 2
silver-brazed
lb/in. (10.342 MPa) lb/in. (10.342 MPa)
filter is required to pass.
A
Union-end, 803-1385943 3000 803-1385943 3000
2 2
silver-brazed
3.1.20 hydrostatic shell test pressure, n—the hydrostatic test lb/in. (20.684 MPa) lb/in. (20.684 MPa)
A
Union-end, 803-1385884 6000 803-1385884 6000
pressure that the filter is required to withstand without damage.
2 2
butt/socket weld
lb/in. (41.369 MPa) lb/in. (41.369 MPa)
The filter must be capable of meeting all performance require-
Other, as specified as specified as specified
ments after the shell test pressure has been removed.
A
For union inlet and outlet connections, only the pertinent dimensions listed in the
applicable documents (military specification or NAVESArequirements) shall apply.
3.1.21 media migration, n—any material released into the
The filter shall be supplied with the thread pieces only, without the tail pieces and
flow stream by the filter media and its materials of construc-
union nuts.
tion. This term refers to the tendency of the filter media or
F1791−00 (2019)
(42.4 mm), 1 ⁄2 NPS (48.3 mm), and 2 NPS (60.3 mm) or as 6.1.2 Design Construction Requirements:
specified in Section 5 (see Table 2). 6.1.2.1 General Construction—The filter shall have a bolted
flanged body and filter bowl to expedite removal of the filter
4.4 End Connections—Filters shall have inlet and outlet end
element for cleaning or replacement.
connections selected from those listed in Table 1 and specified
6.1.2.2 Collapse Strength—The filter element shall be ca-
in Section 5. Inlet and outlet connections shall be identical.
pable of withstanding a differential pressure equal to the
4.5 Contamination Removal Ratings—Filters shall have
maximum inlet pressure rating without structural degradation.
contamination removal ratings selected from the following
6.1.2.3 Automatic Bypass—When specified (see 5.1.4), the
three categories: 20 µm nominal/50 µm absolute, 5 µm
filter assembly shall incorporate an automatic bypass feature to
nominal/18 µm absolute, and 0.4 µm nominal/5 µm absolute.
bypass system fluid automatically around the filter element in
The contamination rating selected shall be specified in Section
the event of excessive flow restriction through the filter
5.
element. The automatic bypass shall be set in accordance with
Table 3 and shall have a capacity equal to or greater than that
5. Ordering Information
of a clean filter assembly.
5.1 Ordering documentation for filters under the specifica-
6.1.2.4 Filter Element Installation—Positive means shall
tion shall include the following information, as required, to
prevent any play or looseness of the filter element in service
describe the equipment adequately.
and prevent cocking or misalignment during installation.
5.1.1 ASTM designation and year of issue,
6.1.2.5 Filter Element Flow Direction—The filter element
5.1.2 Title, number, and date of this specification,
flow direction shall be from the outside to the inside surface of
5.1.3 Filter element type (see 4.1.1),
the element.
5.1.4 Filter element bypass composition (see 4.1.2),
6.1.2.6 Cleanability—Cleanable filter elements shall be
5.1.5 Filter element differential pressure indicator style (see
cleanable and reusable by means of scrubbing and washing the
4.1.3),
outside surface with detergent and tap water and blowing
5.1.6 Filter pressure rating (see 4.2),
through with compressed air not exceeding 30-psig (207-kPa
5.1.7 Size (see 4.3),
gage pressure). Once cleaned, the element shall be capable of
5.1.8 End connections (see 4.4),
meeting the requirements for a new element. Cleanable filter
5.1.9 Contaminant removal rating, absolute/nominal (see
elements shall not be adversely affected by immersion in water
4.5),
and shall be capable of meeting the above criteria for not less
5.1.10 Maximum filter operating pressure,
than five cleaning and reuse cycles.
5.1.11 Flow capacity required (see 7.1, S1.3),
6.1.2.7 Differential Pressure Indicator—When specified
5.1.12 Supplementary requirements, if any (S1.0 through
(see 5.1.5), the filter body shall incorporate a nonelectrical,
S4.0), and
“pop up” differential pressure indicator which senses the
5.1.13 Maximum vibration frequency and amplitude, if
pressure drop across the element and actuates in accordance
other than specified (see S1.8).
withTable3.Onceactuated,aredindicatorbuttonshallremain
up until manually reset.
6. Filter Design and Construction
6.1.2.8 O-Ring Locations—O-rings in face-seal applications
6.1 Filters shall incorporate the design features specified in
shall have the grooves located in the lower members to
6.1.1 – 6.1.6.
simplify assembly.
6.1.1 Materials of Construction—Materials shall be 300
6.1.2.9 Pressure Envelope—The hydrostatic shell test pres-
series corrosion-resistant steel (SS304, 304L, 316, or 316L), or
sures shall be 1.5 times the filter rated pressure at 100°F
other materials selected to provide compatibility with the line
(38°C).
medium, weldability, and corrosion resistance without requir-
ing painting, coating, or plating. The filter body and the filter TABLE 3 Filter Pressure Drop Requirements
bowl shall be weld repairable. Materials for contacting parts
NOTE 1—Percentages shown above shall read as percent of the
shallbeselectedtominimizeelectrolyticcorrosionandgalling.
operating pressure of the filter (see 3.1.23 and 5.1.10).
Filter Pressure Drop
Maximum
Maximum
∆ P Indica- Allowable Filter Element Bypass (see S1.0)
Allowable
tor Contami
Clean Ele-
Actuation -nated Ele-
ment (see
(see 7.1.5) ment (see Set Full Flow Reseat
TABLE 2 Filter Performance Characteristics
7.1.5)
7.1.5)
Minimum Dirt-Holding Capacity
2.5 % 4.75 to 6.25% 7.25to8% 8.25to 6.25 to 7 %
Filter Size, NPS
Grams AC Coarse
5.25 % 9.25 %
⁄4 (13.5 mm) 6.0
⁄2 (21.3 mm) 6.0
Example:
⁄4 (26.9) 10.0 Operating pressure: 1000 psi (6895 kPa)
1 (33.7 mm) 12.0
Maximum allowable clean element pressure drop: 25 psi (172 kPa)
1 ⁄4 (42.4 mm) 12.0 ∆P indicator actuation: 47.5 to 52.5 psi (327 to 346 kPa)
1 ⁄2 (48.3 mm) 14.0
Maximum allowable contaminated element pressure drop: 62.5 psi (431 kPa)
2 (60.3 mm) 16.0 Filter element bypass set pressure drop: 72.5 to 80 psi (500 to 552 kPa)
As specified as specified
Filter element bypass full-flow pressure drop: 82.5 to 92.5 psi (569 to 638 kPa)
Filter element bypass reseat pressure drop: 62.5 to 70 psi (431 to 483 kPa)
F1791−00 (2019)
6.1.2.10 Connections—The inlet and outlet end connections components shall not be required. There shall be no postas-
of the filter shall be as specified in Table 1. Any exposed sembly lubrication required.
threads shall be protected by plastic caps for shipping.
7. Performance
6.1.2.11 Port Configuration—The filter body shall have
7.1 Filters shall meet the performance requirements of 7.1.1
in-line inlet and outlet end connections for installation into the
– 7.1.8.
piping system.
7.1.1 Contaminant Removal Rating—The filter shall be
6.1.2.12 Pressure Lines—All pressure lines in the filter shall
capable of the levels of contaminant removal specified in the
be internally ported.
ordering information (see 4.5 and Section 5).
6.1.2.13 Accessibility—The filter shall be fully and easily
7.1.2 Flow Capacity—The flow capacity of the filter shall
accessible for cleaning or repair without removal of the filter
be as specified in 5.1.11 in standard cubic feet per minute
body from the line.
(cubic metre per second) [at 60°F (16°C) and 14.7 psia (101
6.1.2.14 Threads—Threads shall be as specified in ASME
kPa absolute)]. The filter shall meet the specified maximum
B1.1. Where necessary, provisions shall be incorporated to
flow capacity, or any intermediate capacity, and shall operate
prevent the accidental loosening of threaded parts. The design
whileprovidingthespecifiedfiltercontaminantremovalrating.
shallbesuchthatstandardwrenchescanbeusedonallexternal
Ifanautomaticbypassisspecified(see5.1.4),itshallalsomeet
bolting. Lock-wire shall not be used.
the flow capacity requirements of the filter.
6.1.2.15 Interchangeability—The entire filter, including all
7.1.3 External Leakage—Filter external leakage shall be
associatedpieceparts,shallhavepartnumberidentityandshall
bubble-tight at operating pressure conditions over a 3-min
be replaceable from stock or the manufacturer on a nonselec-
period.
tive and random basis. Parts having the same manufacturer’s
7.1.4 Filter Element Contaminant-Holding Capacity—Solid
part number shall be directly interchangeable with each other
particulate contaminant (dirt) holding capacity shall be as
with respect to installation (physical) and performance (func-
specified in Table 2.
tion). Physically interchangeable assemblies, components, and
7.1.5 Pressure Drop—The maximum allowable filter ele-
parts are those that are capable of being readily installed,
ment clean and contaminated pressure drops shall be as
removed, or replaced without alteration, misalignment, or
specified in Table 3.
damage to parts being installed or adjoining parts. Fabrication
7.1.6 Differential Pressure (∆P) Indicator Actuation
operations such as cutting, filing, drilling, reaming,
Pressure—The pressure drop across the filter element at which
hammering, bending, prying, or forcing shall not be required.
the differential pressure indicator, where applicable, actuates
6.1.2.16 Nonmetallic Element Interchangeability— shall be as specified in Table 3.
Nonmetallic elements, including but not limited to, cushions 7.1.7 Filter Element Bypass Set, Full-Flow, and Reseat
andO-rings,shallbetreatedasseparatelyidentifiedandreadily Differential Pressures—The set, full-flow, and reseat differen-
replaceable parts.
tial pressures of an automatic filter element bypass, where
applicable, shall be as specified in Table 3.
6.1.2.17 Pressure Gage Ports—The filter shall be provided
7.1.8 Media Migration—There shall be no media migration.
with threaded gage connection ports to permit attachment of
pressure gages for sensing the inlet and outlet pressures. The
8. Tests Required
gage connections shall be located to measure the pressure
8.1 Each filter shall pass the tests outlined in 8.1.1 – 8.1.4.
differential across the filter element accurately.
8.1.1 Visual Examination—The filter shall be examined
6.1.2.18 Springs—Any spring incorporated in the filter shall
visually to determine conformance with the ordering data and
not be compressed solid during operation. Spring ends shall be
workmanship without disassembly.
squared and ground. Engagement or disengagement of parts
8.1.2 Hydrostatic Shell Test—The filter shall be hydrostati-
against spring compression shall not be required.
cally tested by applying pressure equal to 1.5 times the 100°F
6.1.3 Maintainability—The filter shall permit direct access
(38°C) rated pressure to the inlet and outlet ports, respectively,
for disassembly, repair, and reassembly of the filter element
to check the structural integrity of the filter. The filter element
and all internal working parts and subassemblies when
may be removed for this test. Pressure shall be applied for a
mountedforoperationinthesystem.Maintenanceshallrequire
minimum of 3 min. Air or nitrogen gas may be used in lieu of
standard tools to the maximum extent possible. Any special
water providing appropriate safety precautions are taken to
tools required for maintenance shall be identified and shall be
minimize the risk associated with the use of a compressible
supplied as part of the filter.
gas. There shall be no external leakage, permanent distortion,
6.1.4 Reversibility—The filter element, and all other parts in
or structural fai
...