KChetan,

Shaft seals of rotary valves are purged to prevent emission of internal gases and dust to the atmosphere. Please clarify if this is the kind of rotary valve purge for which you are looking for design criteria.

Regards,

Amrit Agarwal

Pneumatic Conveying Consulting ■

Dear KChetan,

Purge gas is supplied to maintain a positive flow into the rotary valve. For this, purge gas pressure is controlled so that it is higher than the pressure inside the rotary valve. Since purge gas is generally supplied from a plant header, the header pressure is reduced by a pressure reducing valve.

Purge gas flow rate is based on maintaining a velocity of about 5 ft/sec in the shaft seals. This flow is controlled by a flow control valve. Use of a visual fow indicator is a good idea to make sure that the purge gas is indeed flowing from both sides of the rotary valve.

Regards,

Amrit Agarwal

Pneumatic Conveying Consulting

Email: polypcc@aol.com ■

Chetan,

Purge gas pressure can be set at 10% more than the rotary valve internal pressure but it can be easily increased by the PCV if it is found to be low.

Purge gas flow (cf/sec) is = Purge gas velocity (5ft/sec) x Cirumferential annular area of the shaft seals (ft2).

Regards,

Amrit Agarwal

Pneumatic Conveying Consulting ■

Originally Posted by adithyarevankar

Sir, How do we calculate the compressed air requirement for jet pulse bagfilter

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Dear Adithyarevankar,

You can calculate the compressed air requirements as follows:

1. Find out the diameter of the internal opening of the diaphragm valve through which air flows into the manifold. It should be 1/2 inch, or 3/4 inch, or 1 inch. Now calculate the area of this opening (A).

2. Find out the setting of the air supply pressure (P2)to the diaphragm valve. It is generally in the range of 4o to 70 psig.

3. Get the value of the orifice constant (C) for the valve opening. It should be about 0.5.

4 Assume that the manifold pressure before the valve opens is atmospheric (P1).

To calculate the flow, use the equation : Flow Q = C A [2 g (P2 - P1)]**0.5 ( cu ft/sec)

5.Find out the pulse time, (duration of the pulse, (i.e., time the diaphragm valve is open). It should be about 0.1 second.

Pulse air flow = 0.1 X Q for each manifold 6.

Now find out the no. of manifolds (N)

7. Pulse air flow to all manifolds (To the Dust Colector) = Q X N Cu ft/sec

Regards,

Amrit Agarwal

Pneumatic Conveying Consulting

Email: polypcc@aol.com ■

Dear Sir,

Could you please elaborate the relation between the bag filter fabric total area and the required purge air volume Liter/Sec?

is there any table for this?

and how can i assume the required purging air volume to calculate the tank volume and choose the valves?

thanks for your co-operation..

Ahmed Saad

a.saad@amdind.com

Originally Posted by Amrit Agarwal

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Dear Adithyarevankar,

You can calculate the compressed air requirements as follows:

1. Find out the diameter of the internal opening of the diaphragm valve through which air flows into the manifold. It should be 1/2 inch, or 3/4 inch, or 1 inch. Now calculate the area of this opening (A).

2. Find out the setting of the air supply pressure (P2)to the diaphragm valve. It is generally in the range of 4o to 70 psig.

3. Get the value of the orifice constant (C) for the valve opening. It should be about 0.5.

4 Assume that the manifold pressure before the valve opens is atmospheric (P1).

To calculate the flow, use the equation : Flow Q = C A [2 g (P2 - P1)]**0.5 ( cu ft/sec)

5.Find out the pulse time, (duration of the pulse, (i.e., time the diaphragm valve is open). It should be about 0.1 second.

Pulse air flow = 0.1 X Q for each manifold 6.

Now find out the no. of manifolds (N)

7. Pulse air flow to all manifolds (To the Dust Colector) = Q X N Cu ft/sec

Regards,

Amrit Agarwal

Pneumatic Conveying Consulting

Email: polypcc@aol.com

■

Ahmed Saad;84931]Dear Sir,

Could you please elaborate the relation between the bag filter fabric total area and the required purge air volume Liter/Sec?

is there any table for this?

and how can i assume the required purging air volume to calculate the tank volume and choose the valves?

thanks for your co-operation..

Ahmed Saad

[email]a.saad@amdind.com

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Dear Ahmed,

I think you are mixed up between the flow of purge air and pulse air. Bag filters are mostly of the jet-pulse type. I think you need the flow of pulse air for these dust collectors.

I have already given in a previous post shown above how to calculate the total pulse air flow. Please use that method for your calculations.

Regards,

Amrit Agarwal

Consulting Engineer

Pneumatic Conveying Consulting

Email: polypcc@aol.com ■