压力表培训(荷兰)

Thread quality on the sockets
There will be 3 different threads on the sockets that Stiko BV will place on order: ¼” BSP, ½”BSP and ½” NPT. To check the thread quality for the BSP threads is a straight forward operation with the appropriate thread gauges, see picture.
Most pressure gauges of this type have always the same type of internal parts. In the two pictures the following parts can be identified:
coiled tube (100bar+) C-tube movement min. stop max. stop movement
welding
Alignment of socket, housing and dial plate
The imaginable centerline through the middle of the socket-dial plate- dial and housing should match together. It is an error if the dial plate is off center in the housing despite the fact that the instrument and its internal parts may function well. It is possible to re-align the dial plate with special tooling and should be done before packing and shipment.
Wrong!
2
The gauge is screwed onto the ½”NPT thread the end of the thread should be between the two steps as can be seen in the picture below:
OK!
3 The gauge screws on past the last step. The tread is an absolute reject because it will never seal on the installation.
natural look of stainless steel
All stainless steel industrial pressure gauges
Quality aspects of all stainless steel industrial pressure gauges
Introduction.
Pressure gauges for the industry are generally made according to the European Norm EN 837-1. This EN 837-1 norm gives a lot of details regarding the construction and dial plates on the pressure gauges. For those interested in the details there is a copy of this norm added in the back of this paper. For the purpose of this paper I will limit the details to what is of interest to Stiko. The most frequent ranges seen on the regular pressure gauges are: -1/0 bar -1/+1.5bar -1/+5bar -1/+15 0 / 1.0 0 / 2.5 0 /6 0 /16 0 /40 0 /100 0 /250 -1/+0.6bar -1/+3bar -1/+9bar 0/ 0.6 0 /1.6 0 /4 0 /10 0 /25 0 /60 0 /160 0 /400
Wrong!
Notice: to avoid expensive production losses the threads should be checked before the sockets are welded onto the bourdon tubes or housings!
Gasket surface
Housing made of stainless steel with natural industrial looks, without dents or scratches. Bayonet made of stainless steel with polished surface (STIKO look). It is important that the glass seals accurate on the housing. Check if the bayonets are fitted tightly! There has to be a filling plug on top of the housing to enable customers to do a liquid fill without problems.
Max. stop Unfortunately most internal parts cannot be seen or checked when the instrument is ready so you have to rely on the manufacturer for its quality. Of importance is that the two screws that fasten the movement to the socket are tight. The S-link has to have some movement in upward direction to avoid friction. If there is an error on these items it will show up as irregular or bad movement of the pointer. Also when the two screws are not tight the repeatability of the pointer around the zero mark will be bad.
Only the BSP threads have a gasket surface. This should be a flat and smooth surface without sharp edges or burrs.
Spigot
Spigot
The spigot serves to avoid the gasket ring closing off the opening of the socket when the instrument is fitted on an installation. In general only BSP threads have spigots. The spigot should be machined according to specifications and drawing . As an optional the spigot can have an internal M4 thread to accept a dampening screw. Stiko BV will usually order all their gauges with ½”BSP and ¼”BSP with this M4 thread, but WITHOUT the screw itself.
The BSP thread is a reject if the thread gauge has a sloppy fit or is difficult or even impossible to screw on.
The ½”NPT is a tapered thread that seals on its outside threaded circumference. To assure a good sealing of this thread it is very important the dimensions are machined according to the standards for this thread. The quality of this machining can be checked by the ½”NPT thread gauge. The ½”NPT thread gauge has a stepped thickness, see picture. When the ½”NPT thread gauge is screwed on there are 3 possibilities : 1 the thread screws on but does not reach the first step. The thread should be re-cut to proper dimensions.
Imaginable centerlines
Mid-range
Dial center
plastic cover on thread
For protection during transport a plastic cover is fitted over the threaded part.
Housing and bayonet ring
Thread M4
Welding of socket to housing
The welding of the socket to the housing should look clean (NO stains) and made in a regular uninterrupted way all around the socket. Usually this can be checked with a quick visual inspection.
Before the quality checks are made, the threads should be clean so the thread gauge can be screwed on the thread. Warning: NEVER apply force to screw a thread gauge on the thread! The quality control of a BSP thread is a simple one: just screw the appropriate gauge on the thread see picture.
S-link
S-link SocΒιβλιοθήκη Baiduet
Following two pictures show details of a stainless steel pressure gauge movement with max. and min. stop. Max. stop Min. stop S-link