what is the difference between the check valve & back pressure valve work in the disch. line of metering pump?

Answer 1

In an LMI metering pump the check valves are on the diaphram (pump) unit. These check valves rely on a difference in fluid pressure across the valve in order to operate and seat fully. If you took one off the pump and shook it you would hear the ball rattling around.

The back pressure valve is similar to the ball check except it has a spring which holds the ball against its seat. The liquid pressure must rise above the spring force inorder to raise the ball off its seat and liquid flow. It is usally mounted on the process pipe and is where the chemical enters the system.

LMI also has an optional diaphram back pressure valve which mounts directly on the pump head. This is to aid in the seating of ball check valves by increasing the differential pressure across the check balls. It also has a small bypass/beeder which removes the backpressure to aid in priming the pump.

The back pressure valve has several functions.
1.) It prevents siphoning and uncontrolled flow through the chem feed pump. This would occurr because of either high flow rates passing across the chem feed inlet to the pipe or because the liquid in the pipe is at a slight vacuum. The spring is sized so as to require a substantially higher pressure to open than what could be generated by a siphon.

2.) The back pressure valve causes the chem pump to operate at a higher discharge pressure (because of the spring loading) this higher pressure also aids the seating of the non-spring loaded check valves.

3.) The back pressure valve mounted on the process water pipe also serves as a check valve. This allows the chem feed line and chem pump to be disconnected temporarily without having process water back flow. This allows for quicker replacement of the pump head without shutting down the entire system.

Answer 2

Back Pressure Valve

Answer 3

A check valve is a mechanical device, a valve, that normally allows fluid (liquid or gas) to flow through it in only one direction. Check valves are two-port valves, meaning they have two openings in the body, one for fluid to enter and the other for fluid to leave. There are various types of check valves used in a wide variety of applications. Check valves are often part of common household items. Although they are available in a wide range of sizes and costs, many check valves are very small, simple, and/or cheap. Check valves work automatically and most are not controlled by a person or any external control; accordingly, most do not have any valve handle or stem. The bodies (external shells) of most check valves are made of plastic or metal.

An important concept in check valves is the cracking pressure which is the minimum upstream pressure at which the valve will operate. Typically the check valve is designed for and can therefore be specified for a specific cracking pressure.

Back Pressur Valve:
A type of check valve, typically installed in the tubing hanger, to isolate the production tubing. The back-pressure valve is designed to hold pressure from below yet enable fluids to be pumped from above, as may be required for well-control purposes.

Answer 4

The pressure regulator only operates when the fuel pump is running. So I would have to believe that the check valve is leaking if you are losing fuel pressure overnight. But you'll get a 10 point answer from a knowledgeable mechanic.

Answer 5

Check valve allows flow in one direction only. If two pumps are connected in parallel , the pump which is stand by doesn't rotate in the reverse direction due to check valve which has been installed in the circuit when another pump is in operation.
Back pressure valve operates when the upstream end pressure is more than downstream. Down stream pressure could be Back Pressure.

Answer 6

Check valve ( one way flow valve ) may have self spring loaded so it allow to flow through once got enough pressure to push the check valve. If there is no flow then it will seal off wether there is back pressure or not. that is like sure seal.

Back pressure valve does need pressure to seal.

Answer 7

One is a one way valve -- the other is a flow regulator...

Answer 8

One is for back pressure, and the other is for checking.