Bomba De Circulacion

NPSH required (NPSHr) and tips

What factors should be taken into account in NPSH required? What are the top tips for conducting a diffusion pump system efficient?

Topic: Tips for the installation of metering pumps

Source: Hidrofluidos

Hidrofluidos

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Usually supports add online charging losses to internal NPSH required of the pump. You can deduct losses in static NPSH available online.

- Internal NPSH required: internal NPSH required of a metering pump is generally not taken into account in case of inviscid fluids.

- Effects of inertia (DH): inertia losses are dominant. You can consider NPSH r = DH

The following formula gives the maximum value of the depression generated by the pump at the start of the suction phase:

DH expressed in meter liquid column (mcl) with:

L: length of the suction pipe (m)

Q: maximum rated flow. Pump (l / h)

N: nominal dose rate (gpm)

d: inner diameter of the suction pipe (mm).

Check NPSH

Installation is good, low NPSH standpoint, if the NPSHd exceeds the NPSHr. Given the particular nature of the dosing pumps generally retained security equal to 2 mcl be checked that:

Installation Tips-Importance of Accessories

Suction

A short suction pipe, large diameter, limiting the elbows and avoiding the "swan neck" favors the suction conditions.

- Foot valve - artichoke. Indispensable from the time that the pump is installed "on aspiration." Minimizes the risk of restriking and is provided with a filter element.

- Filter. Imperative when the pump is installed "in charge". Prevents accumulation of solid particles in the valve boxes, thereby guaranteeing precision and durability.

Pressure pipe

The discharge pipe should be as direct as possible. Its sizing and accessories will be determined according to the terms of service.

- Cane injection. Mounted on the injection site, acts as a check valve. Crea, moreover, a backpressure that prevents eventual artificial siphoning.

- Check valve (calibrated valve or back pressure). Artificial creates a back to be regulated in order to avoid any over-flow.

- Safety valve. Located in the drive circuit, protects the metering pump to the pipe and fittings, in the event of accidental overpressure (eg valve closing).

- Damper. Gas Backup Device compressible flow pulsations damps pressure and usually generated by the pump. Is necessary in the discharge pipes of great length, and for pumping high cadences. Requires minimal backpressure of about 1 bar (relative) and should be placed as close to the pump.

Schemes correct types of facilities

The main ways to install correctly diffusion pumps are:

- Pump, "in vacuum" above the tank is equipped with a foot valve (priming). Pipes are short for both suction and discharge, the aspiration is vertical and of a diameter at least equal to the nominal diameter of the pump. Reed injection isolates the pump and the main fluid reagent.

- A nominal pump cadence high (above 140 gpm) often requires the placement of a damper to the drive and optionally a check valve, from the moment the pipe length exceeds 10 m. Provide a suction line as short as possible.

- The placement of buffer systems need long lengths of pipe (chimney balancing, shock ...). Valve creates a back artificial least 1 bar, it is not necessary if the natural pressure is higher.

- Natural siphoning avoided thanks to the calibrated valve which must be adjusted in order to contain the pressure differential. Pump is said "in charge", and it is good to provide for a suction valve and a filter.

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