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New sensor material – Hastelloy

Validyne Engineering now offers an optional sensor body construction in Hastelloy C276.  This greatly improves the corrosion resistance of transducers used in applications where highly oxidizing chemicals are present in the process media.  Along with a teflon-coated sensing diaphragm and wide selection of O-ring materials, the Hastelloy C276 transducer is the most corrosion-resistant transducer ever offered by Validyne Engineering.

Hastelloy C276 is a nickel-chromium-molybdenum alloy that has been proven in over 50 years of service in corrosive environments.  According to the data sheet by Haynes International, the manufacturer of Hastelloy C276: “With its high chromium and molybdenum contents, it is able to withstand both oxidizing and non-oxidizing acids, and exhibits outstanding resistance to pitting and crevice attack in the presence of chlorides and other halides. Furthermore, it is very resistant to sulfide stress cracking and stress corrosion cracking in sour, oilfield environments.”

Other Validyne sensor materials include 316 SST, but Hastelloy C276 does much better where strong acids in high concentrations are present.  From the Haynes International Data sheet:

“To compare the performance of HASTELLOY® C-276 alloy with that of other materials, it is useful to plot the 0.1 mm/y lines. In the following graphs, the lines for C-276 alloy are compared with those of two popular, austenitic stainless steels (316L and 254SMO), and a lower-molybdenum nickel alloy (625), in hydrochloric and sulfuric acids. At hydrochloric acid concentrations above about 5%, C-276 alloy provides a quantum improvement over the stainless steels, and offers much greater resistance to higher concentrations of both acids than alloy 625. The concentration limit of 20% hydrochloric acid is the azeotrope, beyond which high temperature corrosion tests are less reliable.”

The graphs show that Hastelloy C276 survives higher concentrations and higher temperatures of two common acids than does most grades of stainless steel, given the same corrosion rate of 0.1 mm per year.

The addition of Hastelloy C276 as an optional sensor body material will mean greater reliability of pressure transducers in corrosive applications. The DP15 re-rangable pressure sensors, P55 customizable pressure transducers and transmitters, DP360/363 high line pressure sensors and the P365 high line pressure transducers and transmitters all offer Hastelloy C276 as an option for sensor material.

testing stress on blades

Testing Blade Flex

Helicopters are a common sight in the sky and are used for many important tasks.  Rotors are used to provide lift and the large blades on these rotor assemblies often rotate at a rate of 300 RPM or higher, depending on the helicopter type.  The rotor blades must be strong, yet flexible – the attack angle of the blade is varied by the pilot to maneuver the helicopter in flight.

Helicopter rotor blades are dynamic devices, but a static test is typically performed during manufacture to verify the strength and mechanical properties.  The rotor blade is mounted horizontally to a stationary fixture at one end, and a hydraulic ram is affixed to the other end.  A series of LVDTs displacement sensors are arranged along the length of the blade and a strain gage load cell inserted between the hydraulic ram and the tip of the blade.  As pressure is applied to the ram, it flexes the blade.  The force applied to the blade is sensed by the load cell and the LVDTs measure the amount of bending in the blade.  The ratio of applied force to the amount of bending over the length of the rotor blade is an important measure of its strength and flexibility.

The Validyne UPC2100 and USB2250 data acquisition systems are used to interface to the sensors. Long stroke LVDTs used to sense displacement can be wired directly to the UPC/USB.  The UPC/USB interface which provides all required AC sensor excitation, demodulation, A/D conversion and records directly in inches of displacement.  Similarly, the full-bridge load cell can be wired directly to the UPC/USB.  All required DC excitation, amplification and A/D conversion is supplied as well as conversion directly into pounds of force for recording.  Ultimately, a graph of force vs displacement at each measurement point along the rotor blade can be created and this is compared with historical data to insure that the blade has the required strength and flexibility. This can be done using the Easy Sense software or on LabVIEW using our free VI drivers.


Precision Viscometry Using Hydraulic Bridge


If you are making complex molecules, how do you know your process is on target? Many petrochemical products contain long polymer chains that can change character quickly with only small deviations in the manufacturing process. Modern pharmaceuticals now include complex proteins and other molecules that are difficult to characterize by conventional methods. How can you be sure your thousand tons of plastic sheeting or that new wonder drug is going to meet spec? One tool to determine the nature of complex molecules is a precision viscometer.

Viscosity is the internal resistance of a fluid to flow. Complex molecules typically interact with each other in a fluid and this can cause telling changes in viscosity. A polymer molecule in one state may have little interaction with its neighbors, and so its characteristic viscosity is low. In another state, the same polymer may interact strongly, and the resulting viscosity will be much higher. Measuring viscosity is often a reliable way to determine the state of complex molecules in a manufacturing process. The precision viscometer is an important analytical tool in both research and production.

A fluid bridge is used to create a viscometer that is highly sensitive to small changes in product viscosity. A dual metering pump is used to pump two fluids along equal lengths of precision tubing. One side of the pump pushes a fluid of known viscosity. The other side of the pump pushes the test fluid along an identical length of tubing at precisely the same rate as the reference fluid. The difference in back pressure due to flow is a measure of the difference in the viscosity of the two fluids. Because one fluid has a known viscosity, the pressure difference observed between the two lengths of tubing can be used to determine viscosity of the test fluid. The differential pressure transducer is plumbed between the two tubes so that the back pressure difference due to fluid flow is measured directly.

A complete precision viscometer includes the pump, tubing, transducer and a computer that calculates the viscosity and displays a plot on the screen.  These analyzers are often used in conjunction with an liquid chromatography column that fractionates polymers at various temperatures.  As these fractions appear in the unknown fluid stream the viscosity is a good indication of the size and character of the polymer fraction.

Validyne provides the differential transducer that includes special chromatographic pressure fittings in the sensor body.  The very low displacement of the transducer is ideal for use in these systems where dead volume is a source of measurement error.


P55 with special chromatographic pressure fitting 

(Option G under Pressure Port – Ordering Information)



P81 with 1/16″ pressure port 


The latest Validyne sensor for precision viscometry – model P81 –  features a 316 SS sensor body that allows use in aqueous solutions typical in pharmaceutical and food processing applications. Contact our sales department at or at 818-886-8488 for more information on these options.

pressure sensor

Engine Air Filter Pressure Drop

Diesel and gasoline engines require a lot of air as part of the internal combustion process.  Anyone who has lifted the hood on their automobile knows that the air coming into a vehicle engine is filtered to keep out road dust and grit from entering the engine cylinders.  All vehicles have an air filter for this purpose and these are commonly made of a paper filtration material, are housed in a plastic or metal can, and can be opened easily for filter replacement.

Military vehicles also have an engine air filter but this is a much more critical component – off road operations tend to involve much more dust and debris than normal driving and should the filter become completely clogged, the engine will stop.  And you don’t want a stalled engine in the middle of a combat operation.

One way to avoid filtration problems is to measure the pressure drop across the air filter at all times during engine operation.  The best design of an engine air filter is one that allows a lot of air to pass with a minimum loss of pressure, and a lot of effort goes into filter design that can provide a large surface area in a small space – even an ordinary air filter contains dozens of folds to achieve this.  But the danger of a filter clogging is too great and the best method of determining how well a filter is operating is to directly measure the pressure drop across it.

The pressure drop across a working air filter is often very small – on the order of a few hundred Pascals, especially at low engine RPM – so a pressure sensor for this purpose must be sensitive to very low pressures.  In addition, the pressure transducer must be rugged enough to function well under the hood of a vehicle where shock, vibration and high ambient temperatures are common.

Validyne has supplied a variant of the P55 pressure transmitter that has been designed for use in military vehicles to measure air filter pressure drop.  The P55 pressure transmitter electronics has been secured with epoxy and a special housing, connector and custom mounting plate provide a sturdy attachment to the air filter enclosure.  The 4-20 mA signal is used by the engine control system to alert the driver when the air filter starts to clog.  This allows for preventative maintenance and a way to avoid stalling the engine in challenging conditions.

Contact an application engineer at or 818-886-8488 for more information on similar applications.

flame instability

Pressure Transmitter to Detect Burner Flame Instability

Large-scale industrial installations such as refineries and chemical plants often have large heaters that are used in the processing of fluids and gases.  Such heaters must now be designed to minimize NOX emissions to meet Federal clean air requirements and much research has gone into finding ways to make the burning process more efficient.

The technology to reduce emissions in large-scale heaters is complex, but for gas-fired heaters part of the solution is to run the natural gas feeding the burners at a reduced pressure to allow for more complete combustion.  But running lower burner gas pressures increases  the risk of a flame-out – and restarting a large heater could cost hours of downtime.

A large oil company that was retrofitting low NOX burners into their heaters decided to design a system that would detect the conditions present in the combustion chamber just before a flame-out.  When a burner flame becomes unstable it wobbles – much like a candle flickers just before going out.  Because the burners are enclosed, the air pressure inside the heater will exhibit a characteristic oscillatory behavior just as the flame begins to fail.  The air pressures inside the heater are low – just a few inches of water – and this pressure will vary at a characteristic frequency of a few Hz just before flame-out.

Validyne developed a version of the DR800 that is sensitive enough to detect the low heater pressures, yet responsive enough to capture the pressure waveform prior to a flame-out condition.  The electronics of the DR800 were modified to pass frequencies up to 50 Hz and the damping circuit was bypassed.  The modified DR800 is capable of passing low pressure variations up to 10 Hz with no distortion.  The DR800 is FM approved as an intrinsically safe device for Class I, Div 2, Groups B, C and D hazardous locations and is ideal for this application in oil refineries.

Pressure Transmitter

The customer developed a signal processing algorithm that detected a pending flame-out condition in their burner from the character of the DR800 signal.   This involves analyzing the  signal for the right combination of frequency and amplitude of air pressure that occurs prior to a flame-out.   When this situation is detected, a warning light is displayed on the operators control panel and action can be taken to avoid a flame-out and time consuming restart.

The major refinery operators – Exxon, Chevron, Union, etc – will be able to develop a detection algorithm suitable for each individual heater configuration.   Another potential market is the burner manufacturers such as Zeeco, John Zink and others, who are purveying low NOX systems.