24 replies to this topic

[Afshin445]

Dear Expert Members,

Do you have any reference/recommendation about valve type selection specially for vent/drain services and aslo strainer drain valve.

Thanks

Edited by Afshin, 06 March 2012 - 11:47 PM.

[Attiq Ahmad]

Dear Afsin,

Valve type selection is based on your process/service requirement, i.e. if you want to remove vapor/gas from some knock out drum at control rate then you'll required a globe valve for vent. On the other hand, if you want to use vent only during start up / shut down / maintenance, then gate valve would be enough.

From your query, it seems that you are talking about vent/drain valves (bleed valves) required for maintenance purpose for which 3/4" gate valve would be enough. Strainer drain valve shall also be 3/4" drain valve because you need it only when you want to drain strainer for cleaning purpose.

Regards,

Attiq

[Afshin445]

<sup>Ahmad,

Thank you for your fast reply. As you already mentioned my concern was bleed valves for maintenance purpose.
I am agree with you about 3/4" size because we need minimum possible valve size for bleeding.But it is not clear to me how we can select valve type?Are we allowed to use gate valves for all of services, regarding pressure,corrosivity,temp,fouling,etc.? As I saw ball valves also used as a bleeder frequently in projects.My question is what is relation between service and valve type?</sup>

[Attiq Ahmad]

Dear Afsin,

Generally, Ball valves are expansive than gate valves. Hence, if you've no specific reason (e.g. client/project spec) for requirement of ball valve, then gate valve is provided as it less costly than ball valve of same spec.

Regards,

Attiq

[Afshin445]

Dera Attiq,

Actually there is no any project requirement for using ball or gate valve. The only difference is for piping class rating 300# and above we can't find any ball valve smaller than DN50, but for gate valve there is no any restriction in valve size.Another thing is according project spec. we need to use DN20 valve for Y-type strainer for piping rating of 150# and 300#, but I am not clear about rating above 300#, can I use same size?

[breizh]

Hi ,
Consider this resource it may support your query .
Breizh

[Afshin445]

Dear Breizh,

Thank you for your reply.I read the attachment, it was very useful,but it dosn't contain any information regarding valve selection based on nature of service e.g. clarity,corrosivity,pressure,etc.Actually I need to select between Ball and Gate for on-off application for seawater service for different pipe rating.Any more detail will be helpful.

Afshin

[Attiq Ahmad]

Dear Afsin,

Gate valve can also be used for higher pressure rating. The only difference is that for high pressure rating (e.g. above 900# rating), we've to provide two gate valves in series (drain service) instead of single drain valve. This is to ensure valve closure for high pressure lines.

Regards,

Attiq

[Afshin445]

Attiq,

I am agree with you about high pressure rating lines.But my main cocern is which type of manual valves is appropriate for drain/vent service in seawater system? If both ball and gate will be availabe in pipe spec. which one should be selected?

Thanks
Afshin

[Attiq Ahmad]

Dear Afsin,

Gate valve should be selected because gate valve would be ecnomical than ball valve.

(You can confirm this from vendor/supplier that gate valve is cheaper than ball valve.)

Regards,

Attiq

[fallah]

Afshin,

As far as i know, for V/D lines in sea water services gate valve is mostly preferred.

Fallah

[Attiq Ahmad]

You can also use DN20 valve for rating above 300#. Type of valve does not change with increase in rating specially for vent/drain service.

[Afshin445]

Hi Attiq/Fallah

Thanks for your fast reply.As I checked there is not too much difference between ball and gate valves price.You can also check this in the following website:
http://thevalveshop.com/
The main advantage of gate valve is it can be used in dirty services rather than ball, but seawater service can't considere as susch a service, in other hand but ball is more easier for operation and operator prefer to using this type of valves.why we need to use gate compare to ball valve for such a clean service?

Thanks
Afshin

Edited by Afshin, 12 March 2012 - 04:06 AM.

[S.AHMAD]

1. There is specific guidelines for selection between ball and gate valve for vent/drain since I have seen both are being used.
2. For seawater services, I personally prefer ball valves.
3. The slight higher cost of ball valve is a trade-in for ease of operation.
4. The only concern for ball valve for vent/drain is because of it quick opening by a single "stroke". It can open by accident or in-inadvertently opened by operator.
5. This is unacceptable for hazardous system such as toxic materials, liquified gases, high pressure system etc. (for this syetem need double block valves)
6. However, for sea water it is not hazardous unless the pressure.is too dangerously high since high pressure water can cut into steel.

Edited by S.AHMAD, 12 March 2012 - 05:02 AM.

[Attiq Ahmad]

Dear Afsin,

You are right that price difference is negligible (due to small size of valve), so this factor will not effect your type selection.

Definitely, Ease of operation lies with ball valve.

To conclude this discusion, both valves can serve the purpose. Having said that, I think that you shouldn't spend too much time on this and provide the valve which is easily available to you.

Regards,

Attiq

[fallah]

Afshin,

The majority of the ball valves have soft seats, usually PTFE, makes them unsuitable for abrasive services. Abrasive materials, may present in sea water, can damage seating surfaces and clog working clearances in ball valves resulting in sticking, jamming and leakage through these valves. Then, gate valves would be more suitable for V/D than ball ones in sea water applications

Fallah

Edited by fallah, 12 March 2012 - 06:11 AM.

[Afshin445]

Ahmad/Attiq/Fallah

Thank you all for your valuable comments.As Fallah said soft seat ball valves are not good option for seawater application, but why we don't use metal seat ball valve?
In this regard,I am agree with Ahmad viewpoint about using ball valve in seawater system, As Attiq mentioned there is not too much diffrerence in cost between ball and gate valves specially for small size valves, but it can give us ease of operation.It seems metal seat ball valve will be good choice for such a service.Please correct me If I am wrong.

Afshin

Edited by Afshin, 12 March 2012 - 09:10 PM.

[fallah]

It seems metal seat ball valve will be good choice for such a service.Please correct me If I am wrong.

Afshin,

Metal seat ball valves may give tight shut off (when are new), but degree of their tightness for V/D lines in sea water service (with probability of abrasive presence) may decrease after use for a period of the time, hence their leak tightness can not be guaranteed.

Fallah

[Afshin445]

Fallah

Have we need any shut-off requirement for V/D services?

Afshin

Edited by Art Montemayor, 29 June 2012 - 08:30 AM.

[Afshin445]

4. The only concern for ball valve for vent/drain is because of it quick opening by a single "stroke". It can open by accident or in-inadvertently opened by operator.

Ahmad,

Normally we provide a blind flange in end of each V/D valves.It can's avoid such a risk for ball valves?

Afshin

Edited by Afshin, 13 March 2012 - 11:29 PM.

[fallah]

Have we need any shut-off requirement for V/D services?

Afshin,

Tight shutoff is a relative description. Normally, other than special services, there is no specific requirement that the V/D valves to be tight shut off but considering these valves are located end of the drain lines it implies they should inherently have a degree of tightness at shut off.

Fallah

[S.AHMAD]

1. Blind flange or cap may be good enough
2, What important is that you understand the hazards and install the right safeguards.

[Profe]

Hi Afshin

Attached you find the Chemical engineering article about Valves.

Good luck.

Attached Files

•  CHE_Facts_0808-Valves.pdf   583.21KB   136 downloads

[Sherif Morsi]

Dear All,

I would prefer the use of ball valves rather than gate valves. There is a clear section for this topic in API 14E.

Of course gate valves are cheaper than ball valves; however when it comes to fluids carrying solid particles such as sand, ball valves are preferred.
Swing check valves can also be used to prevent reverse flow. I only know this type of check valves, if anyone can tell more about that I would appreciate it.
Also, for vent and drain lines, manual globe valves can be used to regulate the flow.

Regards,

[arthurzhuo]

Soft sealing ball valve can not be used to the medium contains solid particle，the seat really easy to wear out to leak in short time using.For normal hard sealing ball valve like ss304 or 316 is better than soft sealing ball valve but the service life is short,too.If the medium contans corrosive matters like salt it's easy to make the sealing face rust and hard to operate,otherwise,the seawater contains sand will wear out valve to leak quickly.

Based on above opinion we suggest you to choose ceramic lined ball valve which can be used to both of abrasive and corrosive medium and last very long service life.Please refer to below product property and performance of the fine ceramic use to produce the valve: