VALFLON Envelope Gasket

VALFLON (PTFE) Envelope Gasket using compressed non-asbestos fiber sheet and expanded graphite sheet in the core. The core design allows for three different types, the N type, S type and H type , with an additional three different jacket shapes.

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VALQUA No.
N7035(N)
Product name
VALFLON envelope gasket [core: N type]
Series
N7035 Series
Type
N type
Features1
Elastic core material such as compressed non-asbestos sheet, coated with PTFE of コ-shaped cross section
Features2
Effective for narrow gasket width and for eliminating accmulation of liquids.

Applicable fluids
Water, Sea water, Hot water, Steam,Crude oil, Alcohol, Animal & vegetable oil, Heat transfer oilGeneral solvent, Weak acid, Weak alkali,Strong oxidizing acid, strong alkali,Air, Nitrogen gas, Inert gas,Exhaust gas,Inflammable gas,Poisonous,Oxygen,
Inappropriate fluid
Application
main ingredient
Color / print
Type
image
Remarks
As special purpose VALFLON™ Envelope Gaskets, products for monomers, for radiation resisting use, and for outer edge welded type are available Further information is available on request.

■ Available ranges

Temperature(℃) Pressure(MPa)
-100〜150 1.5

In case the service temperature exceeds 120°C, be sure to tighten uniformly so as not to apply piping stress on these gaskets. For applications subject to frequent thermal variations or pressure changes, or where maintenance is not facilitated, WHITETIGHT (No.7590 Series) is recommendable.

Temperature and pressure show individual service limit

■ Dimensions

Nominal thickness(mm) Size(mm)
1.6 1000
2.8
3.8

■ Design criteria

Gasket factor ”m” Minimum design
seating stress"y"
(N/mm2
Recommended
tightening stress
(MPa)Liquid
Recommended
tightening stress
(MPa)Gas
3.5 14.7 15.0 20.0

The recommended tightening stress are the pressures required under normal conditions, and correspond to the projected area of the gasket, where fluid pressure is not taken into consideration.

These m, y values are the same as those of fluororesin gaskets specified in JIS B 2206.

■ The fluid-wise available ranges

The fluid-wise available ranges

■ Stress strain characteristics (No.N7030)

Stress strain characteristics (No.N7030)

■ Notes to be observed in design and usage

■Notes to be observed in design and usage■
▼Notes to be observed in design

・Determine the number and size of bolts and gasket dimensions to provide gaskets with sufficient tightening stress, and also design the construction so as to ensure uniform distribution of tightening stress.
・Determine the construction, material and dimensions so that the flange is not likely to cause rotation.
・Consideration shall be given in design to prevent application of excessive thermal stress or piping stress on the joints.
・Piping design shall not allow accumulation of drain or scale at the flange sections.
・Consideration shall be given to prevent transmission of vibration to the joints.
・Although the likelihood of occurrence of cold flow in the VALFLON (PTFE) has been reduced by adopting flexible core materials, prolonged operation or heat cycles may cause bolts to be loosened. Therefore, these gaskets have to be used in locations permitting periodic checks of loose bolts and also allowing appropriate tightening force to be applied.
・When installing these gaskets onto titanium flanges, check to see if fluids to be handled contain chlorine ions, as even a trace amount of chlorine ions may cause crevice corrosion to develop on the titanium surface in contact with the gaskets. To prevent the occurrence of this crevice corrosion, titanium-palladium alloy is recommended.
・The inner diameter of VALQUA No.N7035 Series has a square shape, which serves to eliminate accumulation of liquids, if the gaskets are properly dimensioned to meet the flange inner diameter. For further details, please contact us, as gaskets can be dimensioned to meet the flange inner diameter.
・Even when resin, glass or hard rubber lined flanges comply with JIS flange standards, their inner diameter or the outer diameter in contact with the gaskets are different from the standards. It is therefore necessary to determine the gasket dimensions in conformity with the size of each flange. Further information in this regard is available on request. Also products are available on request, where the joint sheet has a core made of corrugated metallic sheet.

▼Notes to be observed before installation
・Check perpendicularity of the flange and the pipe.
・Shaft alignment of the mating flanges shall be ensured.
・Check for any deformation of flanges.
・When changing only gaskets for the existing equipment or at a piping joint, clean the connecting section and check for any damage, and repair, if required.
・Get off the rust at the flange surface, and repair any dents and dings.
・Pay attention not to give damage to gaskets during storage up to installation, or during installation work.

▼Notes to be observed before installation
・Install the gaskets in a clean environment so as to prevent entry of foreign matters between the gaskets and the flanges.
・If gasket paste is to be used, apply a minimum amount of "VALFLON Paste" uniformly. Also care shall be exercised after application of paste, to prevent adhesion of dust and the like.
・Flange bolts No.1 to 8 as shown on the figure shall be gradually tightened in this order at a time, and repeat this process in four to five steps, so as to finally ensure uniform tightening.
・As the VALFLON™ (PTFE) outer cover is slippery, crush may occur, if an excessive torque has been applied at the time of tightening or if it is not uniformly tightened. And this is particularly the case for smaller diameter ones, so that care should be exercised in tightening so as not to apply gasket stress exceeding 49.0 MPa.
・A small gap between flanges present at the time of gasket replacement would cause the VALFLON™ (PTFE) outer cover to touch the outside diameter of raised face or the flange inside, and fold over. Tightening in this condition may be a cause of leakage. In order to prevent such fold over of the VALFLON™ (PTFE) outer cover, the gasket-outer edge welded type (ODS type) is available. Further information in this regard is available on request.
・ At the time of tightening gaskets, air contained in the core material may be discharged, so that be careful not to mistake it for leakage when a leakage test is performed using soap water. Our recommendation is to check leakage sometime after tightening the gaskets.
・Insufficient tightening force may lead to permeation of soap water for airtightness test or rain water, causing the Non-Asbestos Felt Sheet to soften and squeezed out from the gaskets. In such a case, gasket stress decreases, which may result in leakage.
・At the time of load up or restarting, check for any loose bolts.
・If retightening of gaskets that have once experienced leakage failed in preventing leakage, replace them with new ones.

▼Notes to be observed in storage
・Store these joint sheets in a cool and dark place not subject to direct sunshine, fresh air or ozone.
・Storage selected shall be in a clean environment, free from dust as well as from high temperature & high humidity and corrosive atmosphere.
・If hanged on nails or the like, gaskets may suffer breakage or permanent deformation, so that, as far as practicable, they should be put in a can or wrapped in a polyethylene bag and stored in a paper box.
・Large sized gaskets shall be put between larger plates without rolling and placed horizontal for storage.
・If Felt Sheet got wet with aqueous liquids, its crush strength decreases. It is therefore necessary to keep it dry in a polyethylene bag, and also not to tighten when wet.

■ Upon placing order

■ FAQ

Q. There seems to be cases in fluorocarbon resin envelope gaskets in which fluids permeate through the jacket and damage the core. Do you have any countermeasures for this?

A. Please consult us for countermeasures such as increasing the thickness of the PTFE jacket, making the exposure area thicker (only for N7035) and improving the chemical resistance of the core material.

Q. I want to control the width of the opening in the flange such as with a sheet gasket. How should I do this?

A. Control with width of the opening in the flange is prone to cause a margin of error and an accurate tightening stress cannot be obtained. It is effective for uneven tightening, so please use it in conjunction with control of tightening torque.

Q. Please tell me about the difference in the gasket dimensions between flanges of the JPI and ASME/ANSI standards.

A. JPI basically quotes from ASME/ANSI, so there are cases in which the dimensions differ slightly due to rounding error during the millimeter conversion of the original number. We understand that, in actual use, the function of the gasket is fulfilled to an equivalent degree by both dimensions.

Q. Why does leakage occur during stop or re-operation even though there are no problems during plant operation?

A. Expansion and contraction of the flange, bolt, pipe and the like will occur due to temperature changes. As a result, a tendency of reduced tightening force in the gasket main unit is often observed when the temperature decreases (including low temperature at the time of initial re-operation), and leakage occurs due to relaxation. We therefore generally recommend a retightening of the gasket before re-operation after the first heat addition.

Q. Is retightening effective when leakage occurs?

A. Yes, it is effective. We ask that retightening during leakage be performed after relieving internal pressure. However, there are also points to keep in mind for each product, such as the possibility of damage as a result of temperature-induced hardening in the case of a compressed non-asbestos fiber sheet.

Q. I am not sure which gasket to select, so could you select it for me?

A. If you contact us together with your operating conditions, we will recommend an appropriate product based on our technician's selection.

■ VALQUA HAND BOOK TECHNICAL DATA

■ VALQUA HAND BOOK DIMENSIONAL DATA


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