Two stage flowmeter

A fluid flowmeter comprising:

• a main passage for the flow of a fluid therethrough and defining a central axis;
• swirl means disposed in said main passage and receiving at least a portion of a fluid flowing in the main passage to swirl the fluid about the central axis at a relatively high velocity for forming a low static pressure region about the central axis immediately downstream of said swirl means;
• a secondary passage disposed about the central axis for communicating a portion of the fluid in said main passage upstream of the swirl means with the low pressure region;
• means for sensing said low static pressure;
• means for sensing the pressure of the fluid before the swirl means;
• and
• a bypass passage operative to selectively interconnect a point upstream of said swirl means with a second point downstream of said radially outwardly swirl means adjacent the low pressure region.

A fluid flowmeter comprising:

• a main fluid flow passage having a central axis;
• swirl means disposed in the main passage and receiving at least a portion of the fluid flowing in the main passage to swirl the fluid about the central axis at a relatively high velocity for forming a low static pressure region about the central axis;
• a secondary passage disposed about the central axis concentrically within said main passage for communicating a portion of the fluid in said main passage upstream of the swirl means with the low pressure region;
• means for sensing the low static pressure;
• means for sensing the pressure of the fluid before the swirl means;
• a bypass passage disposed concentrically with and radially outwardly from said main passage, said bypass passage operative to selectively interconnect a point upstream of said swirl means with a second point downstream of said swirl means radially outwardly adjacent the low pressure region;
• and
• valve means associated with said bypass passage and operative to selectively open and close said bypass passage as a function of the rate of fluid flow through said flowmeter, said valve restricting said bypass passage at relatively low flow rates and opening said bypass passage at relatively high flow rates.

A fluid flowmeter comprising:

• a main passage for the flow of fluid therethrough;
• swirl means disposed within said main passage;
• a secondary passage disposed within said main passage for communicating a portion of the fluid upstream of said swirl means to a point downstream of said swirl means adjacent a low static pressure region formed by said swirl means;
• means for sensing the pressure of the fluid in said low static pressure region;
• a bypass passage operative to selectively interconnect a point upstream of said swirl means with a second point downstream of said swirl means;
• and
• means disposed within said bypass passage for sensing the pressure of the fluid before said swirl means.

A fluid flowmeter comprising:

• a main passage for the flow of a fluid therethrough and defining a central axis;
• swirl means disposed in said main passage and receiving at least a portion of a fluid flowing in the main passage to swirl the fluid about the central axis at a relatively high velocity for forming a low static pressure region about the central axis;
• a secondary passage disposed about the central axis for communicating a portion of the fluid in said main passage upstream of the swirl means with the low pressure region;
• means for sensing said low static pressure;
• a bypass passage operative to selectively interconnect a point upstream of said swirl means with a second point downstream of said swirl means;
• and
• means disposed within said bypass passage for sensing the pressure of the fluid before the swirl means.

A fluid flowmeter comprising:

• a main fluid flow passage having a central axis;
• swirl means disposed in the main passage and receiving at least a portion of the fluid flowing in the main passage to swirl the fluid about the central axis at a relatively high velocity for forming a low static pressure region about the central axis;
• a secondary passage disposed about the central axis concentrically within said main passage for communicating a portion of the fluid in said main passage upstream of the swirl means with the low pressure region;
• means for sensing the low static pressure;
• a bypass passage operative to selectively interconnect a point upstream of said swirl means with a second point downstream of said swirl means;
• valve means associated with said bypass passage and operative to selectively open and close said bypass passage as a function of the rate of fluid flow through said flowmeter, said valve restricting said bypass passage at relatively low flow rates and opening said bypass passage at relatively high flow rates;
• and
• means disposed within said bypass passage, upstream of said valve means for sensing the pressure of the fluid before the swirl means.