Static seals Flashcards
A static seal is a seal between:
two stationary parts
Seals which prevent any fluid from leaking from one side of a system to another are called:
positive seals
Seals which control the amount of leakage are called:
non-positive seals
Static seals seal two surfaces which have little or no movement. All static seals are ____ seals
positive
Two ways of sealing two mating surfaces without additional materials is: (2)
- tapered fit
- interference fit
_____ are installed at a joint between stationary surfaces to seal against a pressure load, seal against leakage, and to control position.
Gaskets
Gaskets are sealed by:
Force of compression exerted by the bolts
Note: Must be greater than internal pressure, hydrostatic end force (which pushes the joints apart)
When using gaskets to seal housings, it’s important that the original gasket thickness is known and the same thickness replaced. This avoids changing:
internal clearance
Always consider gasket ___ when replacing gaskets in an axially split pump with wearing rings
thickness
What are these styles of? flat (full) face, raised face (ring), tongue and groove, spigot and recess?
gasket joints
Surfaces must be parallel and regular in finish
Gasket material is designed to conform to machined surfaces or to ___ slightly to fill small irregularities.
flow
The compression of a gasket is greatest at the:
bolt locations
Closer the bolts, more even the compression. Thinner the material, the more bolts you need for even compression
Gasket material should: (3)
- Withstand the bolt load
- Withstand temperature and pressure
- be compatible with the product
This non metallic gasket material is inexpensive. Often impregnated with fillers such as wax and seals well against water, oil, petroleum fuel. Temperature limit is 120°C
Paper
This non metallic gasket material is used in low pressure applications. Can be impregnated with an elastomer. Seals well against water, oil, and solvent. Useable between -30°C and 150°C
Cork
This non metallic gasket material has excellent mechanical properties and resists water and air. Temperature limit is 121°C
Natural rubber
This non metallic gasket material includes a variety of materials such as buna-s, buna-n, butyl, neoprene, nitrile, viton, silicone.
Synthetic rubber
This non metallic gasket material is used today only for special applications like high temperatures and steam turbines
Asbestos
This non metallic, plastic gasket material resists heat, oil and oxidization, but does not perform well at low temperatures. Temperature limit of 232°C
Acrylic
This non metallic, plastic gasket material is nearly chemically inert, performs well in extremely low temperatures. -190°C to 250°C
Teflon
Gaskets are often coloured to show:
thickness
Metallic gaskets are usually used in what applications?
high temperature high pressure
Metallic gaskets can be solid or a:
composite of several materials
Flat, V or U, rectangular, triangular, octagonal, round, oval, spiral-wound, corrugated, embossed, jacketed with a filler core, metallic inner ring and non metallic outer ring are all examples of what?
Metallic gasket cross sections
Metallic gaskets seal by the:
flow or malleability of the gasket when compressed by bolts. Smoother the surface finish, the better the seal
The circular gasket can have two styles: (2)
- Ring style
- Full face
The ring style gasket is preferred because: (2)
- Takes less time to make it
- Easier to install
_____ gaskets are normally supplied pre stamped and formed for a particular application
metallic gaskets
What two methods can be used to draw out a seal? (2)
- Take measurements and draw from those
- hold the gasket material against the face and transfer it with blueing or by drawing
Protect the end of a gasket hole punch with a:
block of wood
What three things should you do before installing a new gasket? (3)
- Remove all of the old gasket
- Check faces for irregularities, smooth if necessary
- Smear a light film of lube on the contact surfaces
An o ring can be a static or a dynamic seal, and is usually made of:
synthetic rubber
An O ring usually does not make a difference to the _______ of machine parts
relative position
Note: the joint is designed so the correct compression of the o ring happens when the two machined surfaces are in contact
The material for a chosen o ring is chosen to: (2)
- resist chemical
- suit temperature
Note: O rings not made of synthetic rubber are marked by the manufacturer
Metallic O rings are used where extreme conditions of:
temperature, pressure, corrosion exist
Multi lobed, square and rectangular cross section “o rings” are often used as gaskets in:
hydraulic equipment
Note: made from the same materials as standard O rings
A _____ is a gasket forming or sealing compound used in zero to low pressure applications. Found in tape, paste, or liquid form.
sealant
Usually used with a gasket to fill minor depressions in sealing surfaces caused by corrosion
______ sealants are mastic (resit) materials which are soft and adhesive. Usually contain plasticizer which allows them to remain soft.
non hardening sealants
_____ sealants are available in a variety of materials such as butyl, acrylic, silicone and polyurethane. These materials contain curing or setting agents which allow them to remain flexible
hardening-flexible sealants
_____ sealants are based on epoxies, polyesters, acrylics, polyamides, or polyvinyl acetates (PVA). Cure to a rigid state. Tend to crack and result in joints that are difficult to remove. Sometimes used to join as well as seal.
Hardening-rigid sealants
____ are a type of sealant. Available in a variety of shapes for different applications, such as edge, sandwich, lap sealing
tapes
