Why is NRV used in pump discharge?

Non Return Valve is a one way valve mainly used to restrict the flow of a fluid in reverse direction so that a fluid flow in a right direction. It is mainly placed at discharge end of a pump,since some time their is chance of back- flow generation and due to this chance of backward pressure generation to a pump.

Why does a centrifugal pump not need a relief valve?

A relief valve is not necessary for a Centrifugal pump because maximum pressure with the discharge closed is only moderately above working pressure.

What would happen if the discharge valve is closed for a positive displacement valve B centrifugal pump Why?

If the discharge valve is closed and there is no other flow path available to the pump, the impeller will churn the same volume of water as it rotates in the pump casing. The vapor can interrupt the cooling flow to the pump’s packing and bearings, causing excessive wear and heat.

How does NRV valve work?

Non-return valves work by allowing media to flow through them in only one direction. These valves have two openings in the body, one for media to enter and the other for media to leave. The main seat of ball NRVs is conically-tapered to guide the ball into the seat and form a positive seal when stopping reverse flow.

Where do you put NRV?

The valve could be a source of a transient flow leading perhaps to severe pressure waves, NRV should be installed directly downstream of the pump in order to protect the pump from any damage due to the consequences of any generated surge pressures.

Why PSV is provided in reciprocating pump?

PSV is provided at the discharge piping to protect the pump and piping in case of inadvertent closure of discharge valve. 3. Also rated discharge pressure is 9.22 Kg/cm2a.

Why do ships use centrifugal pumps?

Centrifugal pumps are one of the most commonly used pumps on the earth with ever growing applications. They are simple and reliable machine of any machinery space. On ship they are the simplest of machinery installed in the engine room. They are unique for its high flow rate at variable dynamic head with less repairs.

Why is it is recommended to run large centrifugal pump with a closed discharge valve?

When the pump is started with no discharge pressure, the flow will go to maximum and power required will go to maximum and the motor will trip on over load. Starting with a closed discharge valve and slowly opening will fill the system so that hydraulic friction will reduce the flow to match the available power.

Why is it a concern if a positive displacement pump is started with the discharge in the closed position?

A positive displacement pump should not operate against a closed valve on the discharge side of the pump because it has no shutoff head like centrifugal pumps do; a positive displacement pump operating against a closed discharge valve continues to produce flow, and the pressure in the discharge line increases until the …

What is bypass flow?

Bypass Flows – A Definition. A simple definition of a “bypass flow” condition is that the term refers to a requirement that water which would otherwise be diverted in priority instead be “bypassed” from the diversion and left in the stream.

How do you use NRV?

It is found by determining the expected selling price of an asset and all the costs associated with the eventual sale of the asset, and then calculating the difference between these two. To put it in formulaic terms, NRV = Expected selling price – Total production and selling costs.