New Kids on the Block

TIPS FROM THE SERVICE BENCH

Phillips and Allen have dominated machine, sheet metal and cap screws for a long time. They are popular, easy to use and easily recognizable. But Phillips and Allen are looking over their shoulders! There are a couple of New Kids on the Block!

The new kids’ names are Torx and Pozidriv. The names may sound foreign but they fit right in the machine screw neighborhood. More surface area and better geometry make these screws more resistant to cam-out — or stripping — as it is more widely known. KNF is still utilizing Phillips and Allen head screws but Torx and Pozidriv are definitely making their presence felt.

TORX

Figure #1 (click to enlarge)

Torx are called “star drive” by some, as the recess resembles a 6 pointed star. The six points of contact engagement allows for higher torque being applied than a conventional Allen hex drive of the same size. Torx sizes are denoted by a T, followed by a number from 1 to 100. Common sizes used for KNF products include T6, T10, T15, and T25.

Various Torx screws and drivers are depicted in Figure #1 (left); shown clockwise (from top-left): various Torx screw heads, Torx handles, Torx driver, Torx black & white image.

POZIDRIV

Figure #2 (click to enlarge)

Pozidriv screws are almost a cousin to Phillips. The Pozidriv (sometimes spelled incorrectly as “Pozidrive”) is actually an improved version of the Phillips screw drive. The name is short for Positive Drive. This screw recess is very easy confused with Phillips if not noticed. Using a Phillips driver for Pozidriv screw recesses can easily result is a stripped head due to the different geometry of the driver itself. The Pozidriv has additional ribs in the driver tip which are received by the secondary web of the Pozidriv screw itself. This extra feature provides more turning strength due to the higher tool engagement. Figure #2 show various Pozidriv screws and drivers; shown clockwise (from top-left): Pozidriv screw heads, Pozidriv handles, Pozidriv driver, black & white image of Pozidriv.

Pozidriv drive bits are designated by the letters “PZ” plus a size code of 0, 1, 2, 3, 4 or 5. Common at KNF are the 0, 1, and 2 sizes. The drivers themselves will have a PZ marking and size code, and possibly the Pozidriv image on the handle butt.

The Pozidriv screws are visually distinguishable from Phillips by a set of radial indents set at 45° from the main cross recess on the head of the screw. These markings are sometime hard to see on plated or treated screws as the treatment may fill in the slighter 45 degree markings.

Please take care to look at these screws carefully before removing for service. Using the right driver will make your servicing quick and efficient. If you are in doubt of which screw is used on your KNF pump, please contact us. We are here for you.

WELCOME TO THE NEIGHBORHOOD

They don’t make things the way the used to, and this can be a good thing, since the latest tools usually incorporate technological advances that improve performance. Please give the “New Kids on the Block” a chance, they are proving to be hard workers!

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Like Oil and Water, and Ethylbenzene?

Chemical Resistance Compatibility

Tips From the Service Bench

Technology TIP

When pumping liquids, you must be sure flow path wetted materials are compatible with intended media. If not researched and tested, issues may arise in the field that may impact product life and maintenance schedules.

While Chemical Compatibility Charts are a good place to start your research, there is typically a standard disclaimer at the bottom that limits their application and places the responsibility on you the buyer, such as:

Warning: The information in this chart is to be used as a guide, ONLY. Although believed to be accurate, actual decisions on material selection need to be thoroughly tested and evaluated by the customer for each specific application. It is the full responsibility of the customer to perform and evaluate the compatibility of materials for their specific requirements. The manufacturer takes no responsibility, etc., etc…


ARE WE COMPATIBLE?

Polymer components exposed to incompatible media can experience swelling or loss of physical properties. When severe, these effects can lead to degradation of pump performance, reduced pump life, leakage, and even pump failure. These issues are avoided with proper material selection. Many pump manufacturers provide a selection of flow path materials to meet most needs, and some provide additional material options for exceptional cases.

TESTING OUR RELATIONSHIP

So, how do you go about testing chemical compatibility? You can get test swatches of possible polymer materials. But, results using test swatches can be less than applicable since they may be much thinner or thicker than the actual parts used in pumps. KNF offers a better way to assist your compatibility decisions, with our Chemical Resistance Test Kit (p/n 173610). This kit contains our most popular head plates and elastomer valves materials. These are actual production parts in current use, so they offer the best test subjects possible. For each material, two parts are supplied – one for resistance testing, the other as a comparison reference. Simple instructions will guide you through the static soak test process.

Chemical Resistance Kit Materials

Kit materials: (1) PEEK (2) PPS (3) PVDF (4) PP (5) FFKM-A (6) FKM (7) EPDM (8) FFKM-B (9) FFKM-C

SUMMARY

In a typical fluidic system, component lifetime will be influenced by several variables beyond simple compatibility of the liquid media, including chemical concentration, liquid temperature, operating pressure, flow rate, and exposure to abrasive materials. A static soak test cannot, therefore, replace a long-term validation test with a pump running in a real system under system parameters. But, a static soak test is well suited as part of an initial screening to identify and eliminate materials which are clearly incompatible with expected liquids.

Contact KNF today for a Chemical Resistant Test Kit and get pumping with confidence!

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Thread Seal Tape, a Fitting Friend

Tips From the Service Bench

By design, vacuum pumps pull gas or liquid in on the inlet side and expel media on the exhaust side. One prevalent issue to avoid, in order to ensure that the pump keeps operating to full potential, is keeping unwanted material out of the pump head and valves.

Many vacuum pump plumbing connections are made with hose connectors and fittings. One standard fitting thread is the National Pipe Thread (NPT). The threads on an NPT fitting are tapered for sealing, and are often used with a thread sealant, such as Thread Seal tape.

A recurring issue seen by our Service Department is loose Thread Seal tape unintentionally ingested into a pump (see photos below). The loose tape gets pulled in by the vacuum and lodges between the valve and valve seat. This can result in a loss of performance in the system and headaches for the pump user. The cause of this reduced performance is often not readily apparent, either.

Figure 1: Actual photos of ingested Thread Seal tape found within pump heads.

Once ingested, tape will not be expelled on its own as the path through the pump head is not designed to allow long/stringy solids to move through it. The removal of the tape debris involves disassembly of the pump head assembly, removal of the tape and re-assembly after inspection of all the components. This is time consuming and can be avoided.

One way to avoid ingested Thread Seal tape is to understand how the tape works in conjunction with the fitting and threaded port hole. The taper on NPT threads allows them to form a seal when torqued, as the flanks of the threads compress against each other. The fittings seal on the actual thread of the fitting and the hole. The fitting does not necessarily have to be installed to full thread depth as it is sealing on the thread itself.

DO’S

Figure 2: Apply Thread Seal tape

• Wrap the tape clockwise (facing the threaded portion) so that it follows the direction that the fitting will be threaded into the port (see Figure 2). Winding the tape in this direction will prevent the tape from unwinding during the tightening process.

• Use a Thread Seal tape that is narrow enough so it does not cover the first two threads of the fitting (see Figure 3). The first of the male fitting threads are the smallest in diameter and any tape wound onto these threads may actually be cut off as the fitting engages. The cut off tape may then be pulled into the pump head by the gas or liquid flow.

Figure 3: Correct application of Thread Seal tape

• Use 2-4 wraps of Thread Seal tape. You may need to adjust the number of wraps due to specific tolerances.

• Start the fitting by hand to ensure no cross threading occurs.

• Tighten according to fitting manufacturer specifications.

DONT’S

Figure 4: Incorrect application of Thread Seal tape

• Don’t wrap the tape covering the bottom of the fitting. Leave two threads free of tape (see Figure 4).

• Don’t feel the need to tighten fitting until the hex is flush. The sealing occurs on the tapered thread. It is OK if a few threads are left visible as long as the fitting is tightened to the manufacturers specified torque.

WRAP UP

Learning to apply Thread Seal tape properly will serve you well. When used properly, Thread Seal tape is a wonderful sealant. It is inexpensive and works in many different applications. It is easy to apply and lubricates the fitting and threaded hole assembly process. It also prevents possible corrosion at this interface and aids fitting removal.

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New KNF Laboratory Products Catalog Available

KNF Neuberger Inc. has recently published an updated Laboratory Products Catalog. The 33-page catalog reflects the newly expanded range of laboratory products offered by KNF Neuberger, Inc. which includes: a complete line of vacuum pumps and accessories, liquid transfer pumps, dosing/metering pumps, rotary evaporators, and vacuum systems.

Organized by application, this comprehensive guide presents the best product selections for rotary evaporation/distillation, degassing, filtration/SPE, fluid aspiration, gel drying, centrifugal concentration, vacuum ovens, multi-user vacuum systems, and metering and transferring liquid. In addition, this piece includes handy product charts for easy comparison.

View the new Laboratory Products Catalog here. Or, request a high-resolution printed version via postal mail by completing the form below.

Selecting the Proper Pressure Control Valve

KNF FDV Valves with PVDF materials

KNF FDV Valves with PVDF materials

Before deciding on the appropriate diaphragm pressure control valve for your application, it is important to first understand some of the basic uses of these devices. Gaining a better understanding of how a pressure control valve works, and determining how one can best suit your specific application, will simplify the selection process.

What Does a Pressure Control Valve Do?

When used in tandem with a pump, a pressure control valve provides more accurate control over the pressure supplied by the pump. Generally, pressure control valves can be used in the following 2 ways, depending on the application:

1) Pressure Control

A pressure control valve can be used to maintain constant back pressure for exact flow rates under free flow conditions, with positive pressure on the inlet side or with varying back pressure, or with the operation under vacuum, etc.

2) Bypass Valve

A pressure control valve can serve as a safety device for protection of a system’s pump, motor, tubing and connections, vessels and other accessories. Installed as a bypass valve, it prevents excessive pressure build up in the system caused by dirt, misuse or other problems.

Read more…