FAQs and Definitions

Frequently Asked Questions

What is the difference between Absolute and Gauge Pressure?

Absolute pressure is zero-referenced against a perfect vacuum, so it is equal to gauge pressure plus atmospheric pressure. Gauge pressure is zero-referenced against ambient air pressure, so it is equal to absolute pressure minus atmospheric pressure.

There are several units of pressure measurement that are used based on your reference point. Some common examples of Absolute reference are Torr and psia. Some examples of Gauge reference are psig and inches of mercury (vacuum).

Do you have any in stock?

Short answer: No, Wasco builds to order as we have over 6000 user customized applications. We stock thousands of components to minimize lead time.

What is your warranty policy?

Based on the variability of our products our warranty is up to 2 years or 2 million cycles, which ever comes first. Please visit our Terms & Conditions for product-specific warranty.

Who can I speak to about technical issues?

We have a dedicated team of on-site engineers that can help answer your technical questions. Fill out this contact form for customer service to connect you to our engineering team.

Where do you ship?

We currently ship everywhere allowed by U.S. law.

Can I pay with credit card?


Are you ISO9001 certified?


Are you CE compliant, UL recognized, and RoHS compliant?

Yes, we are CE compliant, UL recognized, and RoHS compliant.

Do you have distributors?

We sell direct, and we also have some distributors. Please contact Wasco so we can better serve you.

Definitions for Pressure and Vacuum Applications


The limit of deviation from the set point of a pressure or vacuum switch. It is usually a percentage of full scale.

Actuation Point

See "Setpoint"

Adjustable Range

The limits between which the setpoint can be adjusted.

Burst Pressure

Pressure which causes failure of the pressure element, resulting in permanent damage.


One complete sequence of values usually above and below the setpoint, which occurs during a time period.


The difference between the setpoint and the point where the switch re-actuates.

Differential Pressure

A measured pressure difference between two pressure sources.

Electrical Switching Element

Opens or closes an electrical circuit due to a movement from the pressure or vacuum sensing element.


The difference in readings of an instrument when it is approached from two different directions.

Maximum System Pressure

The highest pressure that a switch may safely operate at.

Maximum Operating Pressure

The designed safe pressure limit of a sensing element at which regular use will cause no damage

Normally Closed

Current flows through the switch until the contact is broken by a pressure or vacuum change.

Normally Open

No current flows through the switch until contact is made by a pressure or vacuum change.


Water tight and dust tight enclosure.


Water tight, dust tight, and corrosion resistant enclosure.

Pressure, Absolute

A pressure scale based on PSIA “0” or a perfect vacuum.

Pressure, Ambient

The pressure immediately surrounding a pressure switch.

Pressure, Atmospheric

The pressure caused by the actual weight of the earth’s atmosphere. At sea level, atmospheric pressure equals 14.7 PSI, 30” HG, or 760 Torr.

Pressure, Barometric

Actual atmospheric pressure in a specific location.

Pressure, Burst

The maximum pressure the unit can withstand without causing a release of the application media.

Pressure, Differential

The difference between a reference pressure and a variable pressure.

Pressure, Gauge

Uses atmosphere as a zero reference point so there is no compensation for changes in barometric pressure.

Pressure, Maximum System

Normal system pressure level not including surges and spikes.

Pressure Proof

Pressure in excess of the maximum operating pressure to which the sensor may occasionally be subjected to.

Pressure, Sensing Element

The portion of the pressure switch that moves with a change in system fluid pressure. Wasco, Inc. pressure switches use capsule, diaphragm, and piston sensing elements.

Pressure, Switch

An instrument that converts a pressure change to an electrical function.

Radio Noise

Electromagnetic interference (EMI)

Reset Band

The difference in pressure between the setpoint and the reset point.

Reset Point

The point at which the electrical switching element snaps back to the position it was at prior to initial actuation.

Response Time (Reaction Time)

The amount of time taken between a change in pressure and a change in the electrical signal.


The ability of the switch to actuate repeatedly at the desired set point within the sensors tolerance.


The exact point at where the electrical switching occurs. This is generally expressed in PSI or inches of mercury.

Setpoint Range

The range from which the switch can be set from the lowest to the highest point.

Switching Current, Maximum

The maximum load (amperage) the electrical switch will carry.

Temperature, Ambient

The temperature immediately surrounding a pressure switch.

Temperature, Shift

A change in setpoint due to changes in ambient, or fluid temperatures.


The value pressure of below atmospheric pressure.

Wetted Parts

Components that come in direct contact with the process media.

Working Pressure Range

The pressure range where the sensor can safely operate and still maintain the setpoint