I would like to know untill when is this patent is valid? Is this patent applicable to India?
The previous answer is only partially correct. India indeed became part of the PCT in December 1998, but before that date you could simply follow the national route. So if you search the Indian Patent Office you will find the respective member of this family, patent IN194756, currently in force (valid). The next (and last) renewal fees are due this coming October. The patent, if properly renewed, will expire 23.10.2017.
A patent is a legal document which confers protection within time and space, so if it is a US patent, it is merely a legal document which confers protection only in USA. Nonetheless according to the PCT and other conventions, you may have patents on the same family, i.e., which share the same priority date, which are valid in other countries, namely India.
After checking that specific patent in Esp@cent, it does not appear to be valid in India, as you can see in the family field, i.e., also published as.
No because patents are, with one exception, national titles, so a US patent never can be valid in India, but...one inventor has one year of priority to apply for the same invention in different countries of the world claiming the first filing date called priority date. According to this; this guy has got for his invention a lot of patent documents published around the world: http://worldwide.espacenet.com/publicationDetails/inpadocPatentFamily?CC=US&NR=6067803A&KC=A&FT=D&ND=3&date=20000530&DB=EPODOC&locale=en_EP ..but none in India because India wasn't a designated state in his PCT application WO98/17226 at the EPO (European Patent Office). Regarding the "value" of the patent it is not much according to Mr or Mrs Godot, that qualified that application in his or her Search Report with two Y's combining two documents: US 4908248A and US 4619678A meaning that the "invention" could be considered as the combination of two other prior art inventions.