Anyone interested in learning more about mechanical Valve Interlocks? 1

[InterlockMan]

thread408-153784

As the thread title really...

I have many years experience of working with mechanical Valve Interlocks and I would be very pleased to help with any questions that you might have:

i.e. What are they?, Where to consider using them?, benefits, pitfalls etc

Feel free to ask whatever you like.

 

[quark]

Hi IM,

Thanks for offering your knowledge. The objective of these forums is exactly that and I hope many of us will get benefited from your expertise and knowledge. Meanwhile, I suggest that please write a FAQ on the topic. You can use the option Write your own Valve engineering FAQ in the Your Reply section.

 

[MortenA]

I do have one question: For an offloading system from a pressure vessel - would you say that in interlock system that would ensure that inlet valves to the vessel was closed, that the vessel had been depressurized and that the vent valves were open BEFORE then valves to the offloading pumps could be opened was a "standard" thing?

Best regards

Morten

 

[InterlockMan]

Hi Morten,

Thanks for the question.

This sounds quite a simple mechanical Interlock system from your description above. The Interlock operating keys will follow a 'linear' sequence to complete this task.

I have a question for you now though: Is putting the vessel back on line a reverse of the 'out' sequence. If it needs to be slightly different (if some kind of vessel purging is undertaken for example) a special selector box might need to be introduced that will permit 'non-linear' key sequencing.

I hope that helps.

 

[MortenA]

You dont need to purge the vessel first. There will be a smaller by-pass valve with a flow limting RO around the main block valves since i assume those wont be able to open with max dP.

Best regards

Morten

 

[InterlockMan]

In that case Morten your required Interlock operational sequence is very simple/standard, and requires no other special equipment.

Does anyone else have any questions?

 

[gerhardl]

Hello InterlockMan, thank you for bringing in a new look on an old and safe, purely mechanical solution for safe valve-sequentional operation!

I would like you (or anyone) to briefly comment on the commercial and availability status for mechanical interlocking devices world- wide.

The problems before (15 to 20 years ago) was diveded between the three items: knowledge, deliverytime and price and practical/mechanical adaption to existing valves.

Has something happened the last ten years to make it more easy to use mechanical interlocking devices on a wider range of valves or more extensively than before?

I think we need more use of safe and simpel systems like this, but the resistance before for specification was price and deliverytime, and (as always) a lack of knowledge of possibillities by non-valve engineers (and even among valve specialists).

Comments anyone?

 

[InterlockMan]

Thanks gerhardl: - you have raised some interesting points/questions in your post.

I am not sure though what you mean by "comment on the commercial and availability status for mechanical interlocking devices world- wide." Could you please explain a little more.

Otherwise I would comments as follows:

There have been some good advances in Interlock technology in last 10-15 years, not least in the understanding of end clients and valve specialists as to what they are and the information required to allow design, manufacture, installation and set up/commissioning.

I believe this is due to two main factors 1) The Interlock manufacturers have designed specific valve data fill in sheets that show exactly the information that they require, and 2) cleints and valve specialists have gradually learnt over the years about this technology - mainly through more regular use/exposure.
Subsequently Interlocks are not viewed as the mysterious pieces of equipment that must not be touched as they were a few years ago. In fact many clients now include training at the manufacturers in their annual budget to ensure that the level of awareness not acheived is maintained.

It is also fair to say that the manufacturers have utilised more 'universal fit' technology than in previous years - these have been mostly through design innovation.

Interlocks will remain bespoke engineered items though, so we are unlikely to see off-the-shelf items or fast deleivery times - typically you are looking at 6-10 weeks lead time after they have received the detailed valve dimensions required.

The pricing of Interlocks has long been a debate, but when the safety and economic 'risks' are compared to the overall price, I would say that they are probably reasonably priced.

 

[gerhardl]

InterlockMan, - thank you! No further explanation necessary (either way), you have answered my questions!

 

[InterlockMan]

It is worth pointing out that mechanical (key transfer) Interlocks are now not just limited to manual valves i.e. lever or hand wheel operation.

The manufacturers also have designs to allow the (Inter)locking of actuated valves (pneumatic, electric and hydraulic), isolating switches, vessel closure doors, C02 deluge systems etc.

All of these devices are easily retrofittable and will not invalidate the original equipment manufacturers product warranty.

How they Interlock actuated valves is particularly interesting due to the valve/actautor sizes and the operational torques of the host equipment.

If anyone would like more details on any of these products or designs, please just let me know.