I'm afraid that I have to respond to your question with a question. Do you want an accurate signal from the transducer during the vacuum part of the process? If so, the answer to the original question is "no"!

If the real question was, "Will the transducer be harmed by a vacuum?", then the answer is "no". Remember a full vacuum is 0 psia or -15 psig. Compared to the full scale range of a transducer of 0-500 psig and probably higher, 15 psi is almost nothing. The transducer will barely notice anything different. The construction of the tip and diaphragm is such that a vacuum causes only a tiny fraction of stresses that it is designed to withstand.

"But suppose," I hear you ask, "I want just an indication of vacuum, not absolute accuracy." Now I must become equivocal. It will probably work. We have performed some testing here, on units from our stock, that indicates a fairly accurate negative output corresponding to increasing vacuum, i.e. output becomes more negative as pressure goes below atmospheric. But this depends on a perfectly filled capillary system. In an ideal world, I would have no qualms about recommending melt pressure transducers for these applications. Since reality is often not ideal and the transducer may not be perfect, a fact we do not like to admit, the output in vacuum may not have the same accuracy as it would for a pressure measurement. Nevertheless, most transducers should give a negative signal in vaccum.

Two caveats - Do not try this with an amplified model such as a 2-wire transmitter. The output cannot go below 4 mA enough to be meaningful. Secondly, if there are significant temperature variations in the process the change in tip temperature could cause a much greater change in output than the vacuum.

Perhaps it is time for a little lesson on screw threads! I am sure that everyone knows that "1/2" is the major diameter of the thread in inches and "20" is the number of threads per inch. For those who don't know, the UN refers to United Screw Thread which is one of the thread forms recognized as an American National Standard. The standard further defines the dimensions, shape height, depth, angles, tolerances, etc. of each thread. The "F" following the "UN" designates "Fine-Thread Series". These series (there are also "C" for "Coarse-Thread Series" and "EF" for "Extra-Fine-Thread Series") are particular combinations of diameter and threads per inch that are selected based on the application. For example, Coarse-Thread devices are used for threading into lower tensile strength materials and softer materials or where rapid assembly/disassembly is desirable or where corrosion or damage to threads is likely. The Fine-Thread Series are found in most other applications where the Coarse threads are not appropriate.

The "2A" or "2B" calls out the thread class. Without going into a long dissertation, this defines the tolerances and allowances on all the parameters of the thread. The "_A" classes are for external threads and the "_B" for internal threads. (Now, I hope you see why the transducer is specified with the "-2A" designation and the mounting well is "-2B".) The Class 2 fit is used on most high quality commercial products. Class 1 is looser and used only for rapid assembly/disassembly and where shake or play is not objectionable. Conversely, Class 3 is found on exceptionally high precision products.

Anyone, with an insatiable curiosity, can consult any mechanical engineering handbook for pages of tabulations of all threads, their dimensions and tolerances. I am indebted to the Dynisco Drafting Department for their assistance in providing me with more information than I ever wanted to know about threads.

It seems only fair that we discuss the pressure fitting of the general purpose transducers, after a dissertation on the threads of the standard melt pressure models. This should satisfy the equal time requirement.

Providing a good seal in plumbing connections, where system pressures exceed 10,000 psig, presents a significant challenge. O-rings and gaskets may leak. Pipe threads cannot withstand the forces generated by the high pressures. (Please remember that we must test the units to at least 1.5 times rated pressure for our overpressure specification.) Over 50 years ago, NBS (now NIST) developed a design for high pressure fittings that addresses these issues. This cone and thread style was further refined by Autoclave Engineers and others, but most people in our industry refer to the numbering system used by AE. (In "F250C" the "F" means a female fitting and "250" designates its use for 1/4 inch heavy wall tubing.)

As you can see in the above sketch, the high pressure fitting eliminates the need for sealing material by substituting a small diameter 60° cone as a metal to metal seat. By subjecting the pressure to a limited area, the forces that must be held by the threads is reduced to acceptable levels