Pressure

http://en.wikipedia.org/wiki/Pressure_measurement

In an engine, the pistons traveling downward from TDC create a vacuum so that when the intake valve opens air is sucked into the cylinder. Since the air goes though the carburetion system (carburetor or fuel injection) the air picks up up particles of fuel, somewhere in the 14.x to 1 range for cars driven on the street.

Since a negative pressure is a vacuum, use a vacuum gauge to measure it. We use a vacuum gun at the shop to checking sealing of valve to seat fit. It is capable of pulling 21 inches of vacuum. On a running engine your gauge will read (on a stock engine) somewhere in the 18-20 inches range.

And most of use have a vacuum cleaner for cleaning the carpets around the house, and maybe a shop vac or two, although I have never measured one of them to see what kind of a vacuum they pulled.

What kind of an application are you getting a negative pressure in Humph?

Ken

I think we need a little more information on the type of system to which you are referring.

Steam turbines run at a partial vacuum at the condenser end.

For measurement of negative pressure there is no shortage of people who will be happy to sell you all sorts of fancy gauges.

If you just want something simple, then a manometer made from a long clear plastic hose shaped like a letter "U" with water in the bottom of the "U" may be all you need.

So, what system are we talking about and what pressure differential do you anticipate?

BAB>

measuring negative pressure depends upon the level of pressure. anything from a photohelic to an ion gauge.